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 $54.40   11.690%   $60.7594   $60.76   $60.75   $60.80  
  Purchase #2 $238.74   6.263%   $253.6923   $253.69   $253.70   $253.70  
  Purchase #3 $194.26   4.329%   $202.6695   $202.67   $202.65   $202.70  
  Purchase #4 $167.34   6.673%   $178.5066   $178.51   $178.50   $178.50  
  Purchase #5 $250.33   11.200%   $278.367   $278.37   $278.35   $278.40  
  Purchase #6 $155.94   8.791%   $169.6487   $169.65   $169.65   $169.60  
  Purchase #7 $177.45   6.680%   $189.3037   $189.30   $189.30   $189.30  
  7 purchase totals = $1,238.46       $1,332.9472   $1,332.95   $1,332.90   $1,333.00