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 $180.57   10.631%   $199.7664   $199.77   $199.75   $199.80  
  Purchase #2 $56.46   10.439%   $62.3539   $62.35   $62.35   $62.40  
  Purchase #3 $162.29   8.797%   $176.5667   $176.57   $176.55   $176.60  
  Purchase #4 $152.59   3.709%   $158.2496   $158.25   $158.25   $158.20  
  Purchase #5 $121.43   3.311%   $125.4505   $125.45   $125.45   $125.50  
  Purchase #6 $67.99   6.236%   $72.2299   $72.23   $72.25   $72.20  
  Purchase #7 $214.59   6.202%   $227.8989   $227.90   $227.90   $227.90  
  7 purchase totals = $955.92       $1,022.5159   $1,022.52   $1,022.50   $1,022.60