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 $208.26   6.426%   $221.6428   $221.64   $221.65   $221.60  
  Purchase #2 $248.28   7.306%   $266.4193   $266.42   $266.40   $266.40  
  Purchase #3 $15.84   5.617%   $16.7297   $16.73   $16.75   $16.70  
  Purchase #4 $24.57   9.513%   $26.9073   $26.91   $26.90   $26.90  
  Purchase #5 $168.86   8.121%   $182.5731   $182.57   $182.55   $182.60  
  Purchase #6 $215.72   8.401%   $233.8426   $233.84   $233.85   $233.80  
  Purchase #7 $65.26   5.249%   $68.6855   $68.69   $68.70   $68.70  
  7 purchase totals = $946.79       $1,016.8003   $1,016.80   $1,016.80   $1,016.70