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 $226.85   8.566%   $246.282   $246.28   $246.30   $246.30  
  Purchase #2 $208.32   11.391%   $232.0497   $232.05   $232.05   $232.00  
  Purchase #3 $185.73   12.264%   $208.5079   $208.51   $208.50   $208.50  
  Purchase #4 $53.78   9.783%   $59.0413   $59.04   $59.05   $59.00  
  Purchase #5 $85.45   8.354%   $92.5885   $92.59   $92.60   $92.60  
  Purchase #6 $167.29   7.757%   $180.2667   $180.27   $180.25   $180.30  
  Purchase #7 $14.38   3.815%   $14.9286   $14.93   $14.95   $14.90  
  7 purchase totals = $941.80       $1,033.6647   $1,033.67   $1,033.70   $1,033.60