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 $246.48   8.627%   $267.7438   $267.74   $267.75   $267.70  
  Purchase #2 $86.82   7.794%   $93.5868   $93.59   $93.60   $93.60  
  Purchase #3 $62.87   11.672%   $70.2082   $70.21   $70.20   $70.20  
  Purchase #4 $228.37   4.735%   $239.1833   $239.18   $239.20   $239.20  
  Purchase #5 $226.83   7.856%   $244.6498   $244.65   $244.65   $244.60  
  Purchase #6 $173.55   10.440%   $191.6686   $191.67   $191.65   $191.70  
  Purchase #7 $185.59   12.143%   $208.1262   $208.13   $208.15   $208.10  
  7 purchase totals = $1,210.51       $1,315.1667   $1,315.17   $1,315.20   $1,315.10