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 $71.96   5.538%   $75.9451   $75.95   $75.95   $75.90  
  Purchase #2 $157.71   11.832%   $176.3702   $176.37   $176.35   $176.40  
  Purchase #3 $146.89   7.740%   $158.2593   $158.26   $158.25   $158.30  
  Purchase #4 $68.58   4.182%   $71.448   $71.45   $71.45   $71.40  
  Purchase #5 $89.44   3.143%   $92.2511   $92.25   $92.25   $92.30  
  Purchase #6 $204.64   8.109%   $221.2343   $221.23   $221.25   $221.20  
  Purchase #7 $40.92   12.319%   $45.9609   $45.96   $45.95   $46.00  
  7 purchase totals = $780.14       $841.4689   $841.47   $841.45   $841.50