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 $250.62   10.120%   $275.9827   $275.98   $276.00   $276.00  
  Purchase #2 $29.94   10.290%   $33.0208   $33.02   $33.00   $33.00  
  Purchase #3 $116.60   7.392%   $125.2191   $125.22   $125.20   $125.20  
  Purchase #4 $188.92   9.226%   $206.3498   $206.35   $206.35   $206.30  
  Purchase #5 $84.67   5.808%   $89.5876   $89.59   $89.60   $89.60  
  Purchase #6 $166.37   5.389%   $175.3357   $175.34   $175.35   $175.30  
  Purchase #7 $42.38   4.421%   $44.2536   $44.25   $44.25   $44.30  
  7 purchase totals = $879.50       $949.7493   $949.75   $949.75   $949.70