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 $112.87   11.846%   $126.2406   $126.24   $126.25   $126.20  
  Purchase #2 $32.33   10.695%   $35.7877   $35.79   $35.80   $35.80  
  Purchase #3 $155.80   8.416%   $168.9121   $168.91   $168.90   $168.90  
  Purchase #4 $17.59   3.615%   $18.2259   $18.23   $18.25   $18.20  
  Purchase #5 $169.45   7.724%   $182.5383   $182.54   $182.55   $182.50  
  Purchase #6 $154.54   9.487%   $169.2012   $169.20   $169.20   $169.20  
  Purchase #7 $166.55   10.659%   $184.3026   $184.30   $184.30   $184.30  
  7 purchase totals = $809.13       $885.2084   $885.21   $885.25   $885.10