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 $242.69   9.738%   $266.3232   $266.32   $266.30   $266.30  
  Purchase #2 $215.28   4.833%   $225.6845   $225.68   $225.70   $225.70  
  Purchase #3 $230.32   6.130%   $244.4386   $244.44   $244.45   $244.40  
  Purchase #4 $24.71   12.687%   $27.845   $27.85   $27.85   $27.80  
  Purchase #5 $239.93   8.382%   $260.0409   $260.04   $260.05   $260.00  
  Purchase #6 $161.34   7.218%   $172.9855   $172.99   $173.00   $173.00  
  Purchase #7 $180.86   13.498%   $205.2725   $205.27   $205.25   $205.30  
  7 purchase totals = $1,295.13       $1,402.5902   $1,402.59   $1,402.60   $1,402.50