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 $148.81   3.592%   $154.1553   $154.16   $154.15   $154.20  
  Purchase #2 $56.47   9.802%   $62.0052   $62.01   $62.00   $62.00  
  Purchase #3 $115.27   13.333%   $130.6389   $130.64   $130.65   $130.60  
  Purchase #4 $123.63   7.581%   $133.0024   $133.00   $133.00   $133.00  
  Purchase #5 $175.70   7.115%   $188.2011   $188.20   $188.20   $188.20  
  Purchase #6 $211.66   10.338%   $233.5414   $233.54   $233.55   $233.50  
  Purchase #7 $59.80   6.732%   $63.8257   $63.83   $63.85   $63.80  
  7 purchase totals = $891.34       $965.3700   $965.38   $965.40   $965.30