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 $85.39   8.282%   $92.462   $92.46   $92.45   $92.50  
  Purchase #2 $105.38   9.857%   $115.7673   $115.77   $115.75   $115.80  
  Purchase #3 $52.81   4.350%   $55.1072   $55.11   $55.10   $55.10  
  Purchase #4 $204.35   6.532%   $217.6981   $217.70   $217.70   $217.70  
  Purchase #5 $198.28   8.109%   $214.3585   $214.36   $214.35   $214.40  
  Purchase #6 $207.49   8.564%   $225.2594   $225.26   $225.25   $225.30  
  Purchase #7 $22.56   5.622%   $23.8283   $23.83   $23.85   $23.80  
  7 purchase totals = $876.26       $944.4808   $944.49   $944.45   $944.60