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 $191.69   4.183%   $199.7084   $199.71   $199.70   $199.70  
  Purchase #2 $30.68   11.759%   $34.2877   $34.29   $34.30   $34.30  
  Purchase #3 $10.74   3.511%   $11.1171   $11.12   $11.10   $11.10  
  Purchase #4 $152.39   10.747%   $168.7674   $168.77   $168.75   $168.80  
  Purchase #5 $205.41   10.550%   $227.0808   $227.08   $227.10   $227.10  
  Purchase #6 $216.33   10.441%   $238.917   $238.92   $238.90   $238.90  
  Purchase #7 $71.70   5.161%   $75.4004   $75.40   $75.40   $75.40  
  7 purchase totals = $878.94       $955.2788   $955.29   $955.25   $955.30