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 $227.36   6.223%   $241.5086   $241.51   $241.50   $241.50  
  Purchase #2 $109.56   8.332%   $118.6885   $118.69   $118.70   $118.70  
  Purchase #3 $164.78   5.193%   $173.337   $173.34   $173.35   $173.30  
  Purchase #4 $245.93   13.693%   $279.6052   $279.61   $279.60   $279.60  
  Purchase #5 $100.68   9.170%   $109.9124   $109.91   $109.90   $109.90  
  Purchase #6 $135.42   6.179%   $143.7876   $143.79   $143.80   $143.80  
  Purchase #7 $233.65   8.215%   $252.8443   $252.84   $252.85   $252.80  
  7 purchase totals = $1,217.38       $1,319.6836   $1,319.69   $1,319.70   $1,319.60