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 $118.73   6.103%   $125.9761   $125.98   $126.00   $126.00  
  Purchase #2 $62.86   10.533%   $69.481   $69.48   $69.50   $69.50  
  Purchase #3 $160.97   12.177%   $180.5713   $180.57   $180.55   $180.60  
  Purchase #4 $56.95   12.372%   $63.9959   $64.00   $64.00   $64.00  
  Purchase #5 $236.83   3.685%   $245.5572   $245.56   $245.55   $245.60  
  Purchase #6 $84.31   3.857%   $87.5618   $87.56   $87.55   $87.60  
  Purchase #7 $92.93   5.202%   $97.7642   $97.76   $97.75   $97.80  
  7 purchase totals = $813.58       $870.9075   $870.91   $870.90   $871.10