Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.53   5.210%   $227.8112   $227.81   $227.80   $227.80  
  Purchase #2 $59.77   8.184%   $64.6616   $64.66   $64.65   $64.70  
  Purchase #3 $174.26   13.573%   $197.9123   $197.91   $197.90   $197.90  
  Purchase #4 $117.85   11.615%   $131.5383   $131.54   $131.55   $131.50  
  Purchase #5 $106.57   7.430%   $114.4882   $114.49   $114.50   $114.50  
  Purchase #6 $232.36   6.539%   $247.554   $247.55   $247.55   $247.60  
  Purchase #7 $232.69   7.167%   $249.3669   $249.37   $249.35   $249.40  
  7 purchase totals = $1,140.03       $1,233.3325   $1,233.33   $1,233.30   $1,233.40