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 $208.76   13.387%   $236.7067   $236.71   $236.70   $236.70  
  Purchase #2 $53.90   11.598%   $60.1513   $60.15   $60.15   $60.20  
  Purchase #3 $135.55   4.381%   $141.4884   $141.49   $141.50   $141.50  
  Purchase #4 $82.94   8.643%   $90.1085   $90.11   $90.10   $90.10  
  Purchase #5 $126.43   6.814%   $135.0449   $135.04   $135.05   $135.00  
  Purchase #6 $96.75   5.421%   $101.9948   $101.99   $102.00   $102.00  
  Purchase #7 $131.89   10.140%   $145.2636   $145.26   $145.25   $145.30  
  7 purchase totals = $836.22       $910.7582   $910.75   $910.75   $910.80