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 $96.59   6.130%   $102.511   $102.51   $102.50   $102.50  
  Purchase #2 $198.40   8.391%   $215.0477   $215.05   $215.05   $215.00  
  Purchase #3 $50.29   6.752%   $53.6856   $53.69   $53.70   $53.70  
  Purchase #4 $45.71   8.517%   $49.6031   $49.60   $49.60   $49.60  
  Purchase #5 $130.69   9.456%   $143.048   $143.05   $143.05   $143.00  
  Purchase #6 $180.94   13.629%   $205.6003   $205.60   $205.60   $205.60  
  Purchase #7 $177.57   9.513%   $194.4622   $194.46   $194.45   $194.50  
  7 purchase totals = $880.19       $963.9579   $963.96   $963.95   $963.90