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 $63.89   11.143%   $71.0093   $71.01   $71.00   $71.00  
  Purchase #2 $232.89   9.520%   $255.0611   $255.06   $255.05   $255.10  
  Purchase #3 $69.45   8.422%   $75.2991   $75.30   $75.30   $75.30  
  Purchase #4 $148.95   5.634%   $157.3418   $157.34   $157.35   $157.30  
  Purchase #5 $245.86   5.861%   $260.2699   $260.27   $260.25   $260.30  
  Purchase #6 $189.78   9.788%   $208.3557   $208.36   $208.35   $208.40  
  Purchase #7 $125.68   4.288%   $131.0692   $131.07   $131.05   $131.10  
  7 purchase totals = $1,076.50       $1,158.4061   $1,158.41   $1,158.35   $1,158.50