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 $227.97   12.842%   $257.2459   $257.25   $257.25   $257.20  
  Purchase #2 $95.36   7.419%   $102.4348   $102.43   $102.45   $102.40  
  Purchase #3 $90.81   5.173%   $95.5076   $95.51   $95.50   $95.50  
  Purchase #4 $12.38   12.450%   $13.9213   $13.92   $13.90   $13.90  
  Purchase #5 $49.75   11.853%   $55.6469   $55.65   $55.65   $55.60  
  Purchase #6 $162.89   5.578%   $171.976   $171.98   $172.00   $172.00  
  Purchase #7 $60.63   11.338%   $67.5042   $67.50   $67.50   $67.50  
  7 purchase totals = $699.79       $764.2367   $764.24   $764.25   $764.10