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 $59.85   10.522%   $66.1474   $66.15   $66.15   $66.10  
  Purchase #2 $158.54   11.571%   $176.8847   $176.88   $176.90   $176.90  
  Purchase #3 $65.28   5.473%   $68.8528   $68.85   $68.85   $68.90  
  Purchase #4 $185.92   12.793%   $209.7047   $209.70   $209.70   $209.70  
  Purchase #5 $139.75   4.197%   $145.6153   $145.62   $145.60   $145.60  
  Purchase #6 $140.56   10.269%   $154.9941   $154.99   $155.00   $155.00  
  Purchase #7 $205.33   8.385%   $222.5469   $222.55   $222.55   $222.50  
  7 purchase totals = $955.23       $1,044.7459   $1,044.74   $1,044.75   $1,044.70