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 $146.60   11.362%   $163.2567   $163.26   $163.25   $163.30  
  Purchase #2 $226.49   13.206%   $256.4003   $256.40   $256.40   $256.40  
  Purchase #3 $12.74   10.275%   $14.049   $14.05   $14.05   $14.00  
  Purchase #4 $242.70   9.848%   $266.6011   $266.60   $266.60   $266.60  
  Purchase #5 $32.61   4.661%   $34.13   $34.13   $34.15   $34.10  
  Purchase #6 $28.81   3.518%   $29.8235   $29.82   $29.80   $29.80  
  Purchase #7 $244.97   9.104%   $267.2721   $267.27   $267.25   $267.30  
  7 purchase totals = $934.92       $1,031.5327   $1,031.53   $1,031.50   $1,031.50