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 $89.72   4.606%   $93.8525   $93.85   $93.85   $93.90  
  Purchase #2 $214.38   9.219%   $234.1437   $234.14   $234.15   $234.10  
  Purchase #3 $176.62   6.298%   $187.7435   $187.74   $187.75   $187.70  
  Purchase #4 $202.92   11.258%   $225.7647   $225.76   $225.75   $225.80  
  Purchase #5 $75.91   9.473%   $83.101   $83.10   $83.10   $83.10  
  Purchase #6 $22.88   12.857%   $25.8217   $25.82   $25.80   $25.80  
  Purchase #7 $42.61   12.528%   $47.9482   $47.95   $47.95   $47.90  
  7 purchase totals = $825.04       $898.3753   $898.36   $898.35   $898.30