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 $98.30   5.227%   $103.4381   $103.44   $103.45   $103.40  
  Purchase #2 $111.47   7.242%   $119.5427   $119.54   $119.55   $119.50  
  Purchase #3 $49.72   7.317%   $53.358   $53.36   $53.35   $53.40  
  Purchase #4 $154.31   4.192%   $160.7787   $160.78   $160.80   $160.80  
  Purchase #5 $247.76   13.832%   $282.0302   $282.03   $282.05   $282.00  
  Purchase #6 $15.62   4.228%   $16.2804   $16.28   $16.30   $16.30  
  Purchase #7 $199.97   4.491%   $208.9507   $208.95   $208.95   $209.00  
  7 purchase totals = $877.15       $944.3788   $944.38   $944.45   $944.40