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 $224.78   13.777%   $255.7479   $255.75   $255.75   $255.70  
  Purchase #2 $89.61   7.395%   $96.2367   $96.24   $96.25   $96.20  
  Purchase #3 $118.74   10.730%   $131.4808   $131.48   $131.50   $131.50  
  Purchase #4 $232.91   11.203%   $259.0029   $259.00   $259.00   $259.00  
  Purchase #5 $227.73   6.103%   $241.6284   $241.63   $241.65   $241.60  
  Purchase #6 $69.63   3.108%   $71.7941   $71.79   $71.80   $71.80  
  Purchase #7 $12.77   13.442%   $14.4865   $14.49   $14.50   $14.50  
  7 purchase totals = $976.17       $1,070.3773   $1,070.38   $1,070.45   $1,070.30