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 $96.27   8.794%   $104.736   $104.74   $104.75   $104.70  
  Purchase #2 $113.87   13.417%   $129.1479   $129.15   $129.15   $129.10  
  Purchase #3 $244.90   12.873%   $276.426   $276.43   $276.45   $276.40  
  Purchase #4 $137.75   6.237%   $146.3415   $146.34   $146.35   $146.30  
  Purchase #5 $113.38   9.567%   $124.2271   $124.23   $124.25   $124.20  
  Purchase #6 $244.81   12.139%   $274.5275   $274.53   $274.55   $274.50  
  Purchase #7 $131.71   6.152%   $139.8128   $139.81   $139.80   $139.80  
  7 purchase totals = $1,082.69       $1,195.2188   $1,195.23   $1,195.30   $1,195.00