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 $85.98   11.863%   $96.1798   $96.18   $96.20   $96.20  
  Purchase #2 $62.34   7.303%   $66.8927   $66.89   $66.90   $66.90  
  Purchase #3 $68.97   4.186%   $71.8571   $71.86   $71.85   $71.90  
  Purchase #4 $206.50   8.492%   $224.036   $224.04   $224.05   $224.00  
  Purchase #5 $44.26   13.705%   $50.3258   $50.33   $50.35   $50.30  
  Purchase #6 $233.46   13.351%   $264.6292   $264.63   $264.65   $264.60  
  Purchase #7 $87.41   5.862%   $92.534   $92.53   $92.55   $92.50  
  7 purchase totals = $788.92       $866.4546   $866.46   $866.55   $866.40