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 $205.81   10.147%   $226.6935   $226.69   $226.70   $226.70  
  Purchase #2 $75.55   11.445%   $84.1967   $84.20   $84.20   $84.20  
  Purchase #3 $30.36   11.670%   $33.903   $33.90   $33.90   $33.90  
  Purchase #4 $155.60   5.468%   $164.1082   $164.11   $164.10   $164.10  
  Purchase #5 $109.26   8.705%   $118.7711   $118.77   $118.75   $118.80  
  Purchase #6 $159.97   10.277%   $176.4101   $176.41   $176.40   $176.40  
  Purchase #7 $198.57   8.694%   $215.8337   $215.83   $215.85   $215.80  
  7 purchase totals = $935.12       $1,019.9163   $1,019.91   $1,019.90   $1,019.90