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 $224.91   3.605%   $233.018   $233.02   $233.00   $233.00  
  Purchase #2 $61.88   7.359%   $66.4337   $66.43   $66.45   $66.40  
  Purchase #3 $143.27   4.859%   $150.2315   $150.23   $150.25   $150.20  
  Purchase #4 $63.83   3.720%   $66.2045   $66.20   $66.20   $66.20  
  Purchase #5 $9.98   3.265%   $10.3058   $10.31   $10.30   $10.30  
  Purchase #6 $208.31   3.828%   $216.2841   $216.28   $216.30   $216.30  
  Purchase #7 $18.86   5.749%   $19.9443   $19.94   $19.95   $19.90  
  7 purchase totals = $731.04       $762.4219   $762.41   $762.45   $762.30