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 $175.75   13.504%   $199.4833   $199.48   $199.50   $199.50  
  Purchase #2 $250.63   7.235%   $268.7631   $268.76   $268.75   $268.80  
  Purchase #3 $160.26   7.370%   $172.0712   $172.07   $172.05   $172.10  
  Purchase #4 $52.87   8.446%   $57.3354   $57.34   $57.35   $57.30  
  Purchase #5 $241.51   10.713%   $267.383   $267.38   $267.40   $267.40  
  Purchase #6 $53.83   9.847%   $59.1306   $59.13   $59.15   $59.10  
  Purchase #7 $159.36   5.333%   $167.8587   $167.86   $167.85   $167.90  
  7 purchase totals = $1,094.21       $1,192.0253   $1,192.02   $1,192.05   $1,192.10