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 $54.27   11.704%   $60.6218   $60.62   $60.60   $60.60  
  Purchase #2 $205.54   10.811%   $227.7609   $227.76   $227.75   $227.80  
  Purchase #3 $102.51   4.716%   $107.3444   $107.34   $107.35   $107.30  
  Purchase #4 $134.35   6.679%   $143.3232   $143.32   $143.30   $143.30  
  Purchase #5 $104.39   4.376%   $108.9581   $108.96   $108.95   $109.00  
  Purchase #6 $194.64   4.796%   $203.9749   $203.97   $203.95   $204.00  
  Purchase #7 $46.30   4.344%   $48.3113   $48.31   $48.30   $48.30  
  7 purchase totals = $842.00       $900.2946   $900.28   $900.20   $900.30