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 $70.89   3.759%   $73.5548   $73.55   $73.55   $73.60  
  Purchase #2 $101.50   4.172%   $105.7346   $105.73   $105.75   $105.70  
  Purchase #3 $46.31   10.627%   $51.2314   $51.23   $51.25   $51.20  
  Purchase #4 $240.92   8.295%   $260.9043   $260.90   $260.90   $260.90  
  Purchase #5 $173.87   8.553%   $188.7411   $188.74   $188.75   $188.70  
  Purchase #6 $242.43   10.658%   $268.2682   $268.27   $268.25   $268.30  
  Purchase #7 $12.36   3.522%   $12.7953   $12.80   $12.80   $12.80  
  7 purchase totals = $888.28       $961.2297   $961.22   $961.25   $961.20