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 $108.54   9.290%   $118.6234   $118.62   $118.60   $118.60  
  Purchase #2 $143.75   13.380%   $162.9838   $162.98   $163.00   $163.00  
  Purchase #3 $53.56   6.826%   $57.216   $57.22   $57.20   $57.20  
  Purchase #4 $182.79   3.473%   $189.1383   $189.14   $189.15   $189.10  
  Purchase #5 $236.63   3.801%   $245.6243   $245.62   $245.60   $245.60  
  Purchase #6 $41.74   12.364%   $46.9007   $46.90   $46.90   $46.90  
  Purchase #7 $69.29   9.716%   $76.0222   $76.02   $76.00   $76.00  
  7 purchase totals = $836.30       $896.5087   $896.50   $896.45   $896.40