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 $56.63   11.645%   $63.2246   $63.22   $63.20   $63.20  
  Purchase #2 $94.77   12.627%   $106.7366   $106.74   $106.75   $106.70  
  Purchase #3 $146.53   4.726%   $153.455   $153.46   $153.45   $153.50  
  Purchase #4 $246.94   7.113%   $264.5048   $264.50   $264.50   $264.50  
  Purchase #5 $163.87   13.217%   $185.5287   $185.53   $185.55   $185.50  
  Purchase #6 $19.59   9.144%   $21.3813   $21.38   $21.40   $21.40  
  Purchase #7 $236.54   5.475%   $249.4906   $249.49   $249.50   $249.50  
  7 purchase totals = $964.87       $1,044.3216   $1,044.32   $1,044.35   $1,044.30