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 $194.60   6.206%   $206.6769   $206.68   $206.70   $206.70  
  Purchase #2 $30.98   9.472%   $33.9144   $33.91   $33.90   $33.90  
  Purchase #3 $51.42   9.582%   $56.3471   $56.35   $56.35   $56.30  
  Purchase #4 $67.27   8.168%   $72.7646   $72.76   $72.75   $72.80  
  Purchase #5 $246.61   3.458%   $255.1378   $255.14   $255.15   $255.10  
  Purchase #6 $15.75   6.151%   $16.7188   $16.72   $16.70   $16.70  
  Purchase #7 $19.81   12.116%   $22.2102   $22.21   $22.20   $22.20  
  7 purchase totals = $626.44       $663.7698   $663.77   $663.75   $663.70