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 $50.92   5.237%   $53.5867   $53.59   $53.60   $53.60  
  Purchase #2 $191.33   7.378%   $205.4463   $205.45   $205.45   $205.40  
  Purchase #3 $99.62   10.501%   $110.0811   $110.08   $110.10   $110.10  
  Purchase #4 $182.84   6.312%   $194.3809   $194.38   $194.40   $194.40  
  Purchase #5 $19.46   11.809%   $21.758   $21.76   $21.75   $21.80  
  Purchase #6 $173.63   7.769%   $187.1193   $187.12   $187.10   $187.10  
  Purchase #7 $61.96   11.309%   $68.9671   $68.97   $68.95   $69.00  
  7 purchase totals = $779.76       $841.3394   $841.35   $841.35   $841.40