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 $211.94   11.677%   $236.6882   $236.69   $236.70   $236.70  
  Purchase #2 $103.97   3.802%   $107.9229   $107.92   $107.90   $107.90  
  Purchase #3 $60.44   10.391%   $66.7203   $66.72   $66.70   $66.70  
  Purchase #4 $71.45   11.545%   $79.6989   $79.70   $79.70   $79.70  
  Purchase #5 $129.67   8.204%   $140.3081   $140.31   $140.30   $140.30  
  Purchase #6 $97.44   4.312%   $101.6416   $101.64   $101.65   $101.60  
  Purchase #7 $154.35   7.209%   $165.4771   $165.48   $165.50   $165.50  
  7 purchase totals = $829.26       $898.4571   $898.46   $898.45   $898.40