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 $242.60   11.188%   $269.7421   $269.74   $269.75   $269.70  
  Purchase #2 $215.33   11.622%   $240.3557   $240.36   $240.35   $240.40  
  Purchase #3 $169.70   13.649%   $192.8624   $192.86   $192.85   $192.90  
  Purchase #4 $54.28   8.189%   $58.725   $58.73   $58.75   $58.70  
  Purchase #5 $156.81   13.158%   $177.4431   $177.44   $177.45   $177.40  
  Purchase #6 $28.26   9.230%   $30.8684   $30.87   $30.85   $30.90  
  Purchase #7 $83.98   8.805%   $91.3744   $91.37   $91.35   $91.40  
  7 purchase totals = $950.96       $1,061.3711   $1,061.37   $1,061.35   $1,061.40