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 $57.99   4.344%   $60.5091   $60.51   $60.50   $60.50  
  Purchase #2 $225.40   12.627%   $253.8613   $253.86   $253.85   $253.90  
  Purchase #3 $84.49   4.779%   $88.5278   $88.53   $88.55   $88.50  
  Purchase #4 $39.35   3.154%   $40.5911   $40.59   $40.60   $40.60  
  Purchase #5 $140.71   5.646%   $148.6545   $148.65   $148.65   $148.70  
  Purchase #6 $13.93   10.460%   $15.3871   $15.39   $15.40   $15.40  
  Purchase #7 $113.63   4.710%   $118.982   $118.98   $119.00   $119.00  
  7 purchase totals = $675.50       $726.5129   $726.51   $726.55   $726.60