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 $90.60   8.120%   $97.9567   $97.96   $97.95   $98.00  
  Purchase #2 $12.30   13.698%   $13.9849   $13.98   $14.00   $14.00  
  Purchase #3 $85.71   7.348%   $92.008   $92.01   $92.00   $92.00  
  Purchase #4 $19.30   13.716%   $21.9472   $21.95   $21.95   $21.90  
  Purchase #5 $246.83   4.592%   $258.1644   $258.16   $258.15   $258.20  
  Purchase #6 $236.82   5.694%   $250.3045   $250.30   $250.30   $250.30  
  Purchase #7 $27.46   11.659%   $30.6616   $30.66   $30.65   $30.70  
  7 purchase totals = $719.02       $765.0273   $765.02   $765.00   $765.10