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 $216.41   9.831%   $237.6853   $237.69   $237.70   $237.70  
  Purchase #2 $119.53   5.624%   $126.2524   $126.25   $126.25   $126.30  
  Purchase #3 $52.79   6.659%   $56.3053   $56.31   $56.30   $56.30  
  Purchase #4 $237.55   6.790%   $253.6796   $253.68   $253.70   $253.70  
  Purchase #5 $6.28   7.704%   $6.7638   $6.76   $6.75   $6.80  
  Purchase #6 $38.46   6.397%   $40.9203   $40.92   $40.90   $40.90  
  Purchase #7 $9.81   4.454%   $10.2469   $10.25   $10.25   $10.20  
  7 purchase totals = $680.83       $731.8536   $731.86   $731.85   $731.90