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 $246.38   6.115%   $261.4461   $261.45   $261.45   $261.40  
  Purchase #2 $23.70   9.782%   $26.0183   $26.02   $26.00   $26.00  
  Purchase #3 $124.66   9.337%   $136.2995   $136.30   $136.30   $136.30  
  Purchase #4 $129.29   3.618%   $133.9677   $133.97   $133.95   $134.00  
  Purchase #5 $216.36   11.868%   $242.0376   $242.04   $242.05   $242.00  
  Purchase #6 $44.67   8.243%   $48.3521   $48.35   $48.35   $48.40  
  Purchase #7 $125.34   11.498%   $139.7516   $139.75   $139.75   $139.80  
  7 purchase totals = $910.40       $987.8729   $987.88   $987.85   $987.90