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 $154.80   11.787%   $173.0463   $173.05   $173.05   $173.00  
  Purchase #2 $200.99   8.268%   $217.6079   $217.61   $217.60   $217.60  
  Purchase #3 $206.60   4.836%   $216.5912   $216.59   $216.60   $216.60  
  Purchase #4 $143.60   6.295%   $152.6396   $152.64   $152.65   $152.60  
  Purchase #5 $31.74   12.413%   $35.6799   $35.68   $35.70   $35.70  
  Purchase #6 $141.73   11.517%   $158.053   $158.05   $158.05   $158.10  
  Purchase #7 $104.60   12.853%   $118.0442   $118.04   $118.05   $118.00  
  7 purchase totals = $984.06       $1,071.6621   $1,071.66   $1,071.70   $1,071.60