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 $226.47   8.787%   $246.3699   $246.37   $246.35   $246.40  
  Purchase #2 $208.67   3.107%   $215.1534   $215.15   $215.15   $215.20  
  Purchase #3 $45.30   13.347%   $51.3462   $51.35   $51.35   $51.30  
  Purchase #4 $197.43   11.563%   $220.2588   $220.26   $220.25   $220.30  
  Purchase #5 $126.75   5.674%   $133.9418   $133.94   $133.95   $133.90  
  Purchase #6 $69.60   12.286%   $78.1511   $78.15   $78.15   $78.20  
  Purchase #7 $104.63   7.562%   $112.5421   $112.54   $112.55   $112.50  
  7 purchase totals = $978.85       $1,057.7633   $1,057.76   $1,057.75   $1,057.80