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 $243.50   6.657%   $259.7098   $259.71   $259.70   $259.70  
  Purchase #2 $78.96   9.107%   $86.1509   $86.15   $86.15   $86.20  
  Purchase #3 $12.90   5.608%   $13.6234   $13.62   $13.60   $13.60  
  Purchase #4 $226.41   11.335%   $252.0736   $252.07   $252.05   $252.10  
  Purchase #5 $177.59   12.574%   $199.9202   $199.92   $199.90   $199.90  
  Purchase #6 $194.30   6.138%   $206.2261   $206.23   $206.25   $206.20  
  Purchase #7 $71.40   8.425%   $77.4155   $77.42   $77.40   $77.40  
  7 purchase totals = $1,005.06       $1,095.1195   $1,095.12   $1,095.05   $1,095.10