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 $241.70   5.644%   $255.3415   $255.34   $255.35   $255.30  
  Purchase #2 $216.75   11.749%   $242.216   $242.22   $242.20   $242.20  
  Purchase #3 $163.60   7.388%   $175.6868   $175.69   $175.70   $175.70  
  Purchase #4 $93.67   8.736%   $101.853   $101.85   $101.85   $101.90  
  Purchase #5 $188.48   7.580%   $202.7668   $202.77   $202.75   $202.80  
  Purchase #6 $145.39   13.387%   $164.8534   $164.85   $164.85   $164.90  
  Purchase #7 $213.32   13.396%   $241.8963   $241.90   $241.90   $241.90  
  7 purchase totals = $1,262.91       $1,384.6138   $1,384.62   $1,384.60   $1,384.70