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 $200.71   6.238%   $213.2303   $213.23   $213.25   $213.20  
  Purchase #2 $94.36   5.677%   $99.7168   $99.72   $99.70   $99.70  
  Purchase #3 $20.57   8.477%   $22.3137   $22.31   $22.30   $22.30  
  Purchase #4 $250.69   6.336%   $266.5737   $266.57   $266.55   $266.60  
  Purchase #5 $47.43   11.327%   $52.8024   $52.80   $52.80   $52.80  
  Purchase #6 $55.67   4.105%   $57.9553   $57.96   $57.95   $58.00  
  Purchase #7 $6.98   5.685%   $7.3768   $7.38   $7.40   $7.40  
  7 purchase totals = $676.41       $719.9690   $719.97   $719.95   $720.00