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 $56.61   8.322%   $61.3211   $61.32   $61.30   $61.30  
  Purchase #2 $234.54   9.243%   $256.2185   $256.22   $256.20   $256.20  
  Purchase #3 $46.95   5.494%   $49.5294   $49.53   $49.55   $49.50  
  Purchase #4 $109.73   5.235%   $115.4744   $115.47   $115.45   $115.50  
  Purchase #5 $196.75   6.545%   $209.6273   $209.63   $209.65   $209.60  
  Purchase #6 $132.97   10.281%   $146.6406   $146.64   $146.65   $146.60  
  Purchase #7 $190.73   11.846%   $213.3239   $213.32   $213.30   $213.30  
  7 purchase totals = $968.28       $1,052.1352   $1,052.13   $1,052.10   $1,052.00