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 $62.80   9.222%   $68.5914   $68.59   $68.60   $68.60  
  Purchase #2 $246.61   7.348%   $264.7309   $264.73   $264.75   $264.70  
  Purchase #3 $211.56   6.738%   $225.8149   $225.81   $225.80   $225.80  
  Purchase #4 $29.25   3.643%   $30.3156   $30.32   $30.30   $30.30  
  Purchase #5 $36.62   10.321%   $40.3996   $40.40   $40.40   $40.40  
  Purchase #6 $185.32   5.495%   $195.5033   $195.50   $195.50   $195.50  
  Purchase #7 $42.93   7.401%   $46.1072   $46.11   $46.10   $46.10  
  7 purchase totals = $815.09       $871.4629   $871.46   $871.45   $871.40