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 $249.89   5.760%   $264.2837   $264.28   $264.30   $264.30  
  Purchase #2 $204.31   3.613%   $211.6917   $211.69   $211.70   $211.70  
  Purchase #3 $224.73   8.847%   $244.6119   $244.61   $244.60   $244.60  
  Purchase #4 $161.54   4.200%   $168.3247   $168.32   $168.30   $168.30  
  Purchase #5 $20.73   11.640%   $23.143   $23.14   $23.15   $23.10  
  Purchase #6 $214.60   4.767%   $224.83   $224.83   $224.85   $224.80  
  Purchase #7 $239.26   8.569%   $259.7622   $259.76   $259.75   $259.80  
  7 purchase totals = $1,315.06       $1,396.6472   $1,396.63   $1,396.65   $1,396.60