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 $250.64   6.739%   $267.5306   $267.53   $267.55   $267.50  
  Purchase #2 $234.67   12.131%   $263.1378   $263.14   $263.15   $263.10  
  Purchase #3 $173.39   11.247%   $192.8912   $192.89   $192.90   $192.90  
  Purchase #4 $224.93   4.714%   $235.5332   $235.53   $235.55   $235.50  
  Purchase #5 $65.87   5.135%   $69.2524   $69.25   $69.25   $69.30  
  Purchase #6 $231.77   4.494%   $242.1857   $242.19   $242.20   $242.20  
  Purchase #7 $232.97   5.863%   $246.629   $246.63   $246.65   $246.60  
  7 purchase totals = $1,414.24       $1,517.1599   $1,517.16   $1,517.25   $1,517.10