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 $240.53   10.796%   $266.4976   $266.50   $266.50   $266.50  
  Purchase #2 $168.93   13.793%   $192.2305   $192.23   $192.25   $192.20  
  Purchase #3 $231.30   7.120%   $247.7686   $247.77   $247.75   $247.80  
  Purchase #4 $201.32   11.718%   $224.9107   $224.91   $224.90   $224.90  
  Purchase #5 $90.71   12.115%   $101.6995   $101.70   $101.70   $101.70  
  Purchase #6 $70.81   11.126%   $78.6883   $78.69   $78.70   $78.70  
  Purchase #7 $233.39   13.447%   $264.774   $264.77   $264.75   $264.80  
  7 purchase totals = $1,236.99       $1,376.5692   $1,376.57   $1,376.55   $1,376.60