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 $144.76   13.465%   $164.2519   $164.25   $164.25   $164.30  
  Purchase #2 $102.58   12.302%   $115.1994   $115.20   $115.20   $115.20  
  Purchase #3 $164.48   7.144%   $176.2305   $176.23   $176.25   $176.20  
  Purchase #4 $159.76   5.779%   $168.9925   $168.99   $169.00   $169.00  
  Purchase #5 $134.93   8.169%   $145.9524   $145.95   $145.95   $146.00  
  Purchase #6 $12.79   5.147%   $13.4483   $13.45   $13.45   $13.40  
  Purchase #7 $46.26   3.166%   $47.7246   $47.72   $47.70   $47.70  
  7 purchase totals = $765.56       $831.7996   $831.79   $831.80   $831.80