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 $198.55   8.290%   $215.0098   $215.01   $215.00   $215.00  
  Purchase #2 $94.85   9.754%   $104.1017   $104.10   $104.10   $104.10  
  Purchase #3 $61.45   12.341%   $69.0335   $69.03   $69.05   $69.00  
  Purchase #4 $178.42   9.517%   $195.4002   $195.40   $195.40   $195.40  
  Purchase #5 $63.66   8.605%   $69.1379   $69.14   $69.15   $69.10  
  Purchase #6 $229.29   8.861%   $249.6074   $249.61   $249.60   $249.60  
  Purchase #7 $52.63   7.460%   $56.5562   $56.56   $56.55   $56.60  
  7 purchase totals = $878.85       $958.8467   $958.85   $958.85   $958.80