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 $141.83   5.285%   $149.3257   $149.33   $149.35   $149.30  
  Purchase #2 $129.72   12.578%   $146.0362   $146.04   $146.05   $146.00  
  Purchase #3 $24.75   12.681%   $27.8885   $27.89   $27.90   $27.90  
  Purchase #4 $116.74   7.772%   $125.813   $125.81   $125.80   $125.80  
  Purchase #5 $69.50   5.387%   $73.244   $73.24   $73.25   $73.20  
  Purchase #6 $200.78   13.254%   $227.3914   $227.39   $227.40   $227.40  
  Purchase #7 $69.30   5.824%   $73.336   $73.34   $73.35   $73.30  
  7 purchase totals = $752.62       $823.0348   $823.04   $823.10   $822.90