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 $81.98   12.609%   $92.3169   $92.32   $92.30   $92.30  
  Purchase #2 $245.95   12.280%   $276.1527   $276.15   $276.15   $276.20  
  Purchase #3 $185.34   11.422%   $206.5095   $206.51   $206.50   $206.50  
  Purchase #4 $8.49   8.613%   $9.2212   $9.22   $9.20   $9.20  
  Purchase #5 $153.97   4.729%   $161.2512   $161.25   $161.25   $161.30  
  Purchase #6 $191.68   8.471%   $207.9172   $207.92   $207.90   $207.90  
  Purchase #7 $195.51   5.389%   $206.046   $206.05   $206.05   $206.00  
  7 purchase totals = $1,062.92       $1,159.4147   $1,159.42   $1,159.35   $1,159.40