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 $109.25   4.648%   $114.3279   $114.33   $114.35   $114.30  
  Purchase #2 $230.50   9.631%   $252.6995   $252.70   $252.70   $252.70  
  Purchase #3 $173.44   3.667%   $179.8   $179.80   $179.80   $179.80  
  Purchase #4 $168.25   9.808%   $184.752   $184.75   $184.75   $184.80  
  Purchase #5 $118.41   11.495%   $132.0212   $132.02   $132.00   $132.00  
  Purchase #6 $63.56   3.738%   $65.9359   $65.94   $65.95   $65.90  
  Purchase #7 $176.82   9.739%   $194.0405   $194.04   $194.05   $194.00  
  7 purchase totals = $1,040.23       $1,123.5770   $1,123.58   $1,123.60   $1,123.50