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 $246.41   5.666%   $260.3716   $260.37   $260.35   $260.40  
  Purchase #2 $49.92   11.301%   $55.5615   $55.56   $55.55   $55.60  
  Purchase #3 $174.42   13.214%   $197.4679   $197.47   $197.45   $197.50  
  Purchase #4 $72.46   8.309%   $78.4807   $78.48   $78.50   $78.50  
  Purchase #5 $23.73   13.536%   $26.9421   $26.94   $26.95   $26.90  
  Purchase #6 $194.66   7.766%   $209.7773   $209.78   $209.80   $209.80  
  Purchase #7 $228.94   6.220%   $243.1801   $243.18   $243.20   $243.20  
  7 purchase totals = $990.54       $1,071.7812   $1,071.78   $1,071.80   $1,071.90