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 $56.86   3.817%   $59.0303   $59.03   $59.05   $59.00  
  Purchase #2 $172.72   9.272%   $188.7346   $188.73   $188.75   $188.70  
  Purchase #3 $24.42   8.822%   $26.5743   $26.57   $26.55   $26.60  
  Purchase #4 $165.63   4.487%   $173.0618   $173.06   $173.05   $173.10  
  Purchase #5 $112.96   3.808%   $117.2615   $117.26   $117.25   $117.30  
  Purchase #6 $140.82   5.394%   $148.4158   $148.42   $148.40   $148.40  
  Purchase #7 $114.70   5.391%   $120.8835   $120.88   $120.90   $120.90  
  7 purchase totals = $788.11       $833.9618   $833.95   $833.95   $834.00