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 $118.60   5.131%   $124.6854   $124.69   $124.70   $124.70  
  Purchase #2 $86.26   11.260%   $95.9729   $95.97   $95.95   $96.00  
  Purchase #3 $59.98   13.477%   $68.0635   $68.06   $68.05   $68.10  
  Purchase #4 $96.47   9.729%   $105.8556   $105.86   $105.85   $105.90  
  Purchase #5 $164.81   11.596%   $183.9214   $183.92   $183.90   $183.90  
  Purchase #6 $136.69   12.179%   $153.3375   $153.34   $153.35   $153.30  
  Purchase #7 $175.57   11.425%   $195.6289   $195.63   $195.65   $195.60  
  7 purchase totals = $838.38       $927.4652   $927.47   $927.45   $927.50