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 $248.47   7.609%   $267.3761   $267.38   $267.40   $267.40  
  Purchase #2 $33.63   11.761%   $37.5852   $37.59   $37.60   $37.60  
  Purchase #3 $46.39   11.378%   $51.6683   $51.67   $51.65   $51.70  
  Purchase #4 $154.67   4.664%   $161.8838   $161.88   $161.90   $161.90  
  Purchase #5 $221.77   7.466%   $238.3273   $238.33   $238.35   $238.30  
  Purchase #6 $214.99   9.514%   $235.4441   $235.44   $235.45   $235.40  
  Purchase #7 $13.89   10.390%   $15.3332   $15.33   $15.35   $15.30  
  7 purchase totals = $933.81       $1,007.6180   $1,007.62   $1,007.70   $1,007.60