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 $200.66   6.664%   $214.032   $214.03   $214.05   $214.00  
  Purchase #2 $48.63   9.874%   $53.4317   $53.43   $53.45   $53.40  
  Purchase #3 $37.47   4.498%   $39.1554   $39.16   $39.15   $39.20  
  Purchase #4 $123.54   13.819%   $140.612   $140.61   $140.60   $140.60  
  Purchase #5 $108.26   4.519%   $113.1523   $113.15   $113.15   $113.20  
  Purchase #6 $204.34   12.629%   $230.1461   $230.15   $230.15   $230.10  
  Purchase #7 $240.69   5.418%   $253.7306   $253.73   $253.75   $253.70  
  7 purchase totals = $963.59       $1,044.2601   $1,044.26   $1,044.30   $1,044.20