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 $82.60   10.731%   $91.4638   $91.46   $91.45   $91.50  
  Purchase #2 $239.30   11.392%   $266.5611   $266.56   $266.55   $266.60  
  Purchase #3 $22.73   3.363%   $23.4944   $23.49   $23.50   $23.50  
  Purchase #4 $181.53   6.752%   $193.7869   $193.79   $193.80   $193.80  
  Purchase #5 $44.93   6.505%   $47.8527   $47.85   $47.85   $47.90  
  Purchase #6 $205.48   10.172%   $226.3814   $226.38   $226.40   $226.40  
  Purchase #7 $219.67   4.718%   $230.034   $230.03   $230.05   $230.00  
  7 purchase totals = $996.24       $1,079.5743   $1,079.56   $1,079.60   $1,079.70