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 $236.91   10.669%   $262.1859   $262.19   $262.20   $262.20  
  Purchase #2 $125.35   4.772%   $131.3317   $131.33   $131.35   $131.30  
  Purchase #3 $116.81   13.507%   $132.5875   $132.59   $132.60   $132.60  
  Purchase #4 $25.86   10.628%   $28.6084   $28.61   $28.60   $28.60  
  Purchase #5 $166.74   13.141%   $188.6513   $188.65   $188.65   $188.70  
  Purchase #6 $73.77   3.307%   $76.2096   $76.21   $76.20   $76.20  
  Purchase #7 $37.33   11.871%   $41.7614   $41.76   $41.75   $41.80  
  7 purchase totals = $782.77       $861.3358   $861.34   $861.35   $861.40