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 $61.95   13.763%   $70.4762   $70.48   $70.50   $70.50  
  Purchase #2 $229.60   3.269%   $237.1056   $237.11   $237.10   $237.10  
  Purchase #3 $215.56   8.255%   $233.3545   $233.35   $233.35   $233.40  
  Purchase #4 $108.46   5.431%   $114.3505   $114.35   $114.35   $114.40  
  Purchase #5 $165.43   10.716%   $183.1575   $183.16   $183.15   $183.20  
  Purchase #6 $149.90   4.607%   $156.8059   $156.81   $156.80   $156.80  
  Purchase #7 $24.91   13.786%   $28.3441   $28.34   $28.35   $28.30  
  7 purchase totals = $955.81       $1,023.5943   $1,023.60   $1,023.60   $1,023.70