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 $247.44   6.201%   $262.7838   $262.78   $262.80   $262.80  
  Purchase #2 $152.99   13.370%   $173.4448   $173.44   $173.45   $173.40  
  Purchase #3 $6.64   10.796%   $7.3569   $7.36   $7.35   $7.40  
  Purchase #4 $224.67   10.243%   $247.6829   $247.68   $247.70   $247.70  
  Purchase #5 $46.31   8.745%   $50.3598   $50.36   $50.35   $50.40  
  Purchase #6 $127.68   9.128%   $139.3346   $139.33   $139.35   $139.30  
  Purchase #7 $55.40   8.744%   $60.2442   $60.24   $60.25   $60.20  
  7 purchase totals = $861.13       $941.2070   $941.19   $941.25   $941.20