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 $30.61   7.661%   $32.955   $32.96   $32.95   $33.00  
  Purchase #2 $140.79   7.141%   $150.8438   $150.84   $150.85   $150.80  
  Purchase #3 $68.40   6.646%   $72.9459   $72.95   $72.95   $72.90  
  Purchase #4 $205.69   3.144%   $212.1569   $212.16   $212.15   $212.20  
  Purchase #5 $40.94   8.458%   $44.4027   $44.40   $44.40   $44.40  
  Purchase #6 $15.94   9.242%   $17.4132   $17.41   $17.40   $17.40  
  Purchase #7 $182.56   3.183%   $188.3709   $188.37   $188.35   $188.40  
  7 purchase totals = $684.93       $719.0884   $719.09   $719.05   $719.10