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 $43.67   5.239%   $45.9579   $45.96   $45.95   $46.00  
  Purchase #2 $132.48   6.671%   $141.3177   $141.32   $141.30   $141.30  
  Purchase #3 $16.88   9.560%   $18.4937   $18.49   $18.50   $18.50  
  Purchase #4 $113.85   4.734%   $119.2397   $119.24   $119.25   $119.20  
  Purchase #5 $217.54   8.458%   $235.9395   $235.94   $235.95   $235.90  
  Purchase #6 $184.36   4.351%   $192.3815   $192.38   $192.40   $192.40  
  Purchase #7 $69.65   12.600%   $78.4259   $78.43   $78.45   $78.40  
  7 purchase totals = $778.43       $831.7559   $831.76   $831.80   $831.70