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 $154.97   6.311%   $164.7502   $164.75   $164.75   $164.80  
  Purchase #2 $158.29   11.393%   $176.324   $176.32   $176.30   $176.30  
  Purchase #3 $91.70   10.423%   $101.2579   $101.26   $101.25   $101.30  
  Purchase #4 $233.61   12.165%   $262.0287   $262.03   $262.05   $262.00  
  Purchase #5 $107.66   6.225%   $114.3618   $114.36   $114.35   $114.40  
  Purchase #6 $184.96   6.496%   $196.975   $196.98   $197.00   $197.00  
  Purchase #7 $196.40   7.378%   $210.8904   $210.89   $210.90   $210.90  
  7 purchase totals = $1,127.59       $1,226.5880   $1,226.59   $1,226.60   $1,226.70