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 $86.69   8.232%   $93.8263   $93.83   $93.85   $93.80  
  Purchase #2 $132.42   10.732%   $146.6313   $146.63   $146.65   $146.60  
  Purchase #3 $47.97   5.410%   $50.5652   $50.57   $50.55   $50.60  
  Purchase #4 $217.25   8.774%   $236.3115   $236.31   $236.30   $236.30  
  Purchase #5 $221.27   4.849%   $231.9994   $232.00   $232.00   $232.00  
  Purchase #6 $112.28   12.226%   $126.0074   $126.01   $126.00   $126.00  
  Purchase #7 $240.25   12.386%   $270.0074   $270.01   $270.00   $270.00  
  7 purchase totals = $1,058.13       $1,155.3485   $1,155.36   $1,155.35   $1,155.30