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 $67.87   13.113%   $76.7698   $76.77   $76.75   $76.80  
  Purchase #2 $215.51   9.539%   $236.0675   $236.07   $236.05   $236.10  
  Purchase #3 $136.25   8.659%   $148.0479   $148.05   $148.05   $148.00  
  Purchase #4 $121.68   13.560%   $138.1798   $138.18   $138.20   $138.20  
  Purchase #5 $110.36   7.853%   $119.0266   $119.03   $119.05   $119.00  
  Purchase #6 $123.97   10.792%   $137.3488   $137.35   $137.35   $137.30  
  Purchase #7 $136.38   9.762%   $149.6934   $149.69   $149.70   $149.70  
  7 purchase totals = $912.02       $1,005.1338   $1,005.14   $1,005.15   $1,005.10