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 $216.38   11.614%   $241.5104   $241.51   $241.50   $241.50  
  Purchase #2 $35.77   5.499%   $37.737   $37.74   $37.75   $37.70  
  Purchase #3 $81.68   5.165%   $85.8988   $85.90   $85.90   $85.90  
  Purchase #4 $66.38   11.159%   $73.7873   $73.79   $73.80   $73.80  
  Purchase #5 $15.30   6.196%   $16.248   $16.25   $16.25   $16.20  
  Purchase #6 $215.46   9.452%   $235.8253   $235.83   $235.85   $235.80  
  Purchase #7 $232.60   10.209%   $256.3461   $256.35   $256.35   $256.30  
  7 purchase totals = $863.57       $947.3529   $947.37   $947.40   $947.20