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 $224.69   6.193%   $238.6051   $238.61   $238.60   $238.60  
  Purchase #2 $250.25   4.835%   $262.3496   $262.35   $262.35   $262.30  
  Purchase #3 $184.62   7.129%   $197.7816   $197.78   $197.80   $197.80  
  Purchase #4 $234.48   12.535%   $263.8721   $263.87   $263.85   $263.90  
  Purchase #5 $154.42   6.243%   $164.0604   $164.06   $164.05   $164.10  
  Purchase #6 $213.87   9.843%   $234.9212   $234.92   $234.90   $234.90  
  Purchase #7 $32.66   7.814%   $35.2121   $35.21   $35.20   $35.20  
  7 purchase totals = $1,294.99       $1,396.8021   $1,396.80   $1,396.75   $1,396.80