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 $104.73   8.780%   $113.9253   $113.93   $113.95   $113.90  
  Purchase #2 $69.93   7.217%   $74.9768   $74.98   $75.00   $75.00  
  Purchase #3 $66.78   13.248%   $75.627   $75.63   $75.65   $75.60  
  Purchase #4 $122.26   6.372%   $130.0504   $130.05   $130.05   $130.10  
  Purchase #5 $125.42   5.738%   $132.6166   $132.62   $132.60   $132.60  
  Purchase #6 $232.34   6.461%   $247.3515   $247.35   $247.35   $247.40  
  Purchase #7 $15.60   13.851%   $17.7608   $17.76   $17.75   $17.80  
  7 purchase totals = $737.06       $792.3084   $792.32   $792.35   $792.40