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 $70.39   11.664%   $78.6003   $78.60   $78.60   $78.60  
  Purchase #2 $246.85   8.269%   $267.262   $267.26   $267.25   $267.30  
  Purchase #3 $201.41   5.166%   $211.8148   $211.81   $211.80   $211.80  
  Purchase #4 $220.26   5.163%   $231.632   $231.63   $231.65   $231.60  
  Purchase #5 $162.70   8.798%   $177.0143   $177.01   $177.00   $177.00  
  Purchase #6 $242.77   7.575%   $261.1598   $261.16   $261.15   $261.20  
  Purchase #7 $162.99   12.222%   $182.9106   $182.91   $182.90   $182.90  
  7 purchase totals = $1,307.37       $1,410.3938   $1,410.38   $1,410.35   $1,410.40