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 $68.27   7.553%   $73.4264   $73.43   $73.45   $73.40  
  Purchase #2 $196.57   12.111%   $220.3766   $220.38   $220.40   $220.40  
  Purchase #3 $19.74   4.837%   $20.6948   $20.69   $20.70   $20.70  
  Purchase #4 $239.45   11.856%   $267.8392   $267.84   $267.85   $267.80  
  Purchase #5 $69.29   9.574%   $75.9238   $75.92   $75.90   $75.90  
  Purchase #6 $16.61   6.328%   $17.6611   $17.66   $17.65   $17.70  
  Purchase #7 $185.37   12.431%   $208.4133   $208.41   $208.40   $208.40  
  7 purchase totals = $795.30       $884.3352   $884.33   $884.35   $884.30