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 $26.96   12.759%   $30.3998   $30.40   $30.40   $30.40  
  Purchase #2 $208.42   13.519%   $236.5963   $236.60   $236.60   $236.60  
  Purchase #3 $43.60   11.754%   $48.7247   $48.72   $48.70   $48.70  
  Purchase #4 $54.39   12.848%   $61.378   $61.38   $61.40   $61.40  
  Purchase #5 $221.58   12.284%   $248.7989   $248.80   $248.80   $248.80  
  Purchase #6 $222.45   13.234%   $251.889   $251.89   $251.90   $251.90  
  Purchase #7 $176.38   10.327%   $194.5948   $194.59   $194.60   $194.60  
  7 purchase totals = $953.78       $1,072.3815   $1,072.38   $1,072.40   $1,072.40