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 $29.73   9.296%   $32.4937   $32.49   $32.50   $32.50  
  Purchase #2 $52.42   11.659%   $58.5316   $58.53   $58.55   $58.50  
  Purchase #3 $158.33   11.299%   $176.2197   $176.22   $176.20   $176.20  
  Purchase #4 $249.78   8.837%   $271.8531   $271.85   $271.85   $271.90  
  Purchase #5 $109.59   3.314%   $113.2218   $113.22   $113.20   $113.20  
  Purchase #6 $206.68   4.603%   $216.1935   $216.19   $216.20   $216.20  
  Purchase #7 $245.66   13.607%   $279.087   $279.09   $279.10   $279.10  
  7 purchase totals = $1,052.19       $1,147.6004   $1,147.59   $1,147.60   $1,147.60