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 $171.50   8.278%   $185.6968   $185.70   $185.70   $185.70  
  Purchase #2 $91.63   11.595%   $102.2545   $102.25   $102.25   $102.30  
  Purchase #3 $247.61   4.678%   $259.1932   $259.19   $259.20   $259.20  
  Purchase #4 $239.89   9.587%   $262.8883   $262.89   $262.90   $262.90  
  Purchase #5 $246.96   9.746%   $271.0287   $271.03   $271.05   $271.00  
  Purchase #6 $96.33   6.396%   $102.4913   $102.49   $102.50   $102.50  
  Purchase #7 $27.40   12.452%   $30.8118   $30.81   $30.80   $30.80  
  7 purchase totals = $1,121.32       $1,214.3646   $1,214.36   $1,214.40   $1,214.40