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 $84.72   4.219%   $88.2943   $88.29   $88.30   $88.30  
  Purchase #2 $71.38   12.754%   $80.4838   $80.48   $80.50   $80.50  
  Purchase #3 $140.98   11.560%   $157.2773   $157.28   $157.30   $157.30  
  Purchase #4 $182.46   12.859%   $205.9225   $205.92   $205.90   $205.90  
  Purchase #5 $55.46   13.185%   $62.7724   $62.77   $62.75   $62.80  
  Purchase #6 $249.50   7.332%   $267.7933   $267.79   $267.80   $267.80  
  Purchase #7 $136.26   11.567%   $152.0212   $152.02   $152.00   $152.00  
  7 purchase totals = $920.76       $1,014.5648   $1,014.55   $1,014.55   $1,014.60