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 $60.87   3.629%   $63.079   $63.08   $63.10   $63.10  
  Purchase #2 $47.53   4.658%   $49.7439   $49.74   $49.75   $49.70  
  Purchase #3 $237.44   4.583%   $248.3219   $248.32   $248.30   $248.30  
  Purchase #4 $135.82   3.286%   $140.283   $140.28   $140.30   $140.30  
  Purchase #5 $240.89   6.588%   $256.7598   $256.76   $256.75   $256.80  
  Purchase #6 $215.57   12.139%   $241.738   $241.74   $241.75   $241.70  
  Purchase #7 $192.63   5.309%   $202.8567   $202.86   $202.85   $202.90  
  7 purchase totals = $1,130.75       $1,202.7823   $1,202.78   $1,202.80   $1,202.80