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 $134.92   7.123%   $144.5304   $144.53   $144.55   $144.50  
  Purchase #2 $241.53   6.777%   $257.8985   $257.90   $257.90   $257.90  
  Purchase #3 $24.54   6.451%   $26.1231   $26.12   $26.10   $26.10  
  Purchase #4 $214.38   11.837%   $239.7562   $239.76   $239.75   $239.80  
  Purchase #5 $67.41   11.536%   $75.1864   $75.19   $75.20   $75.20  
  Purchase #6 $84.36   9.535%   $92.4037   $92.40   $92.40   $92.40  
  Purchase #7 $118.36   6.314%   $125.8333   $125.83   $125.85   $125.80  
  7 purchase totals = $885.50       $961.7316   $961.73   $961.75   $961.70