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 $188.44   9.311%   $205.9856   $205.99   $206.00   $206.00  
  Purchase #2 $91.93   6.128%   $97.5635   $97.56   $97.55   $97.60  
  Purchase #3 $241.95   4.674%   $253.2587   $253.26   $253.25   $253.30  
  Purchase #4 $245.36   6.629%   $261.6249   $261.62   $261.60   $261.60  
  Purchase #5 $8.47   8.550%   $9.1942   $9.19   $9.20   $9.20  
  Purchase #6 $175.82   10.704%   $194.6398   $194.64   $194.65   $194.60  
  Purchase #7 $192.68   9.573%   $211.1253   $211.13   $211.15   $211.10  
  7 purchase totals = $1,144.65       $1,233.3920   $1,233.39   $1,233.40   $1,233.40