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 $207.38   3.806%   $215.2729   $215.27   $215.25   $215.30  
  Purchase #2 $63.99   5.681%   $67.6253   $67.63   $67.65   $67.60  
  Purchase #3 $160.94   7.684%   $173.3066   $173.31   $173.30   $173.30  
  Purchase #4 $77.53   9.308%   $84.7465   $84.75   $84.75   $84.70  
  Purchase #5 $212.97   3.192%   $219.768   $219.77   $219.75   $219.80  
  Purchase #6 $56.33   10.724%   $62.3708   $62.37   $62.35   $62.40  
  Purchase #7 $126.70   8.622%   $137.6241   $137.62   $137.60   $137.60  
  7 purchase totals = $905.84       $960.7142   $960.72   $960.65   $960.70