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 $49.63   13.423%   $56.2918   $56.29   $56.30   $56.30  
  Purchase #2 $89.38   4.102%   $93.0464   $93.05   $93.05   $93.00  
  Purchase #3 $208.73   10.865%   $231.4085   $231.41   $231.40   $231.40  
  Purchase #4 $82.95   10.146%   $91.3661   $91.37   $91.35   $91.40  
  Purchase #5 $112.39   11.776%   $125.625   $125.63   $125.65   $125.60  
  Purchase #6 $226.39   10.768%   $250.7677   $250.77   $250.75   $250.80  
  Purchase #7 $99.79   5.571%   $105.3493   $105.35   $105.35   $105.30  
  7 purchase totals = $869.26       $953.8548   $953.87   $953.85   $953.80