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 $55.54   11.211%   $61.7666   $61.77   $61.75   $61.80  
  Purchase #2 $149.51   12.596%   $168.3423   $168.34   $168.35   $168.30  
  Purchase #3 $152.36   9.598%   $166.9835   $166.98   $167.00   $167.00  
  Purchase #4 $9.78   12.310%   $10.9839   $10.98   $11.00   $11.00  
  Purchase #5 $152.48   6.105%   $161.7889   $161.79   $161.80   $161.80  
  Purchase #6 $184.85   5.211%   $194.4825   $194.48   $194.50   $194.50  
  Purchase #7 $96.77   8.674%   $105.1638   $105.16   $105.15   $105.20  
  7 purchase totals = $801.29       $869.5115   $869.50   $869.55   $869.60