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 $91.44   6.330%   $97.2282   $97.23   $97.25   $97.20  
  Purchase #2 $69.68   3.353%   $72.0164   $72.02   $72.00   $72.00  
  Purchase #3 $66.53   12.144%   $74.6094   $74.61   $74.60   $74.60  
  Purchase #4 $186.76   10.170%   $205.7535   $205.75   $205.75   $205.80  
  Purchase #5 $209.67   5.649%   $221.5143   $221.51   $221.50   $221.50  
  Purchase #6 $201.48   6.204%   $213.9798   $213.98   $214.00   $214.00  
  Purchase #7 $126.41   10.263%   $139.3835   $139.38   $139.40   $139.40  
  7 purchase totals = $951.97       $1,024.4851   $1,024.48   $1,024.50   $1,024.50