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 $205.54   10.219%   $226.5441   $226.54   $226.55   $226.50  
  Purchase #2 $156.75   12.770%   $176.767   $176.77   $176.75   $176.80  
  Purchase #3 $66.63   10.510%   $73.6328   $73.63   $73.65   $73.60  
  Purchase #4 $207.53   3.723%   $215.2563   $215.26   $215.25   $215.30  
  Purchase #5 $168.86   12.470%   $189.9168   $189.92   $189.90   $189.90  
  Purchase #6 $108.98   5.812%   $115.3139   $115.31   $115.30   $115.30  
  Purchase #7 $178.61   9.511%   $195.5976   $195.60   $195.60   $195.60  
  7 purchase totals = $1,092.90       $1,193.0285   $1,193.03   $1,193.00   $1,193.00