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 $226.45   11.405%   $252.2766   $252.28   $252.30   $252.30  
  Purchase #2 $233.77   12.175%   $262.2315   $262.23   $262.25   $262.20  
  Purchase #3 $146.54   5.502%   $154.6026   $154.60   $154.60   $154.60  
  Purchase #4 $8.93   5.450%   $9.4167   $9.42   $9.40   $9.40  
  Purchase #5 $242.78   6.352%   $258.2014   $258.20   $258.20   $258.20  
  Purchase #6 $176.38   10.199%   $194.369   $194.37   $194.35   $194.40  
  Purchase #7 $230.74   6.241%   $245.1405   $245.14   $245.15   $245.10  
  7 purchase totals = $1,265.59       $1,376.2383   $1,376.24   $1,376.25   $1,376.20