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 $142.65   11.669%   $159.2958   $159.30   $159.30   $159.30  
  Purchase #2 $189.46   7.858%   $204.3478   $204.35   $204.35   $204.30  
  Purchase #3 $163.38   7.728%   $176.006   $176.01   $176.00   $176.00  
  Purchase #4 $76.53   10.639%   $84.672   $84.67   $84.65   $84.70  
  Purchase #5 $208.77   6.119%   $221.5446   $221.54   $221.55   $221.50  
  Purchase #6 $138.97   13.733%   $158.0548   $158.05   $158.05   $158.10  
  Purchase #7 $38.31   10.772%   $42.4368   $42.44   $42.45   $42.40  
  7 purchase totals = $958.07       $1,046.3578   $1,046.36   $1,046.35   $1,046.30