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 $94.56   9.729%   $103.7597   $103.76   $103.75   $103.80  
  Purchase #2 $21.90   5.593%   $23.1249   $23.12   $23.10   $23.10  
  Purchase #3 $239.38   7.826%   $258.1139   $258.11   $258.10   $258.10  
  Purchase #4 $170.64   9.601%   $187.0231   $187.02   $187.00   $187.00  
  Purchase #5 $68.84   12.600%   $77.5138   $77.51   $77.50   $77.50  
  Purchase #6 $207.96   9.779%   $228.2964   $228.30   $228.30   $228.30  
  Purchase #7 $136.70   5.742%   $144.5493   $144.55   $144.55   $144.50  
  7 purchase totals = $939.98       $1,022.3811   $1,022.37   $1,022.30   $1,022.30