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 $206.66   12.723%   $232.9534   $232.95   $232.95   $233.00  
  Purchase #2 $82.85   10.103%   $91.2203   $91.22   $91.20   $91.20  
  Purchase #3 $38.58   4.186%   $40.195   $40.20   $40.20   $40.20  
  Purchase #4 $250.69   7.245%   $268.8525   $268.85   $268.85   $268.90  
  Purchase #5 $14.49   6.590%   $15.4449   $15.44   $15.45   $15.40  
  Purchase #6 $93.99   3.791%   $97.5532   $97.55   $97.55   $97.60  
  Purchase #7 $182.35   9.540%   $199.7462   $199.75   $199.75   $199.70  
  7 purchase totals = $869.61       $945.9655   $945.96   $945.95   $946.00