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 $114.90   3.564%   $118.995   $119.00   $119.00   $119.00  
  Purchase #2 $154.62   13.529%   $175.5385   $175.54   $175.55   $175.50  
  Purchase #3 $34.35   6.737%   $36.6642   $36.66   $36.65   $36.70  
  Purchase #4 $82.25   3.526%   $85.1501   $85.15   $85.15   $85.20  
  Purchase #5 $193.41   8.600%   $210.0433   $210.04   $210.05   $210.00  
  Purchase #6 $181.49   10.453%   $200.4611   $200.46   $200.45   $200.50  
  Purchase #7 $78.35   7.757%   $84.4276   $84.43   $84.45   $84.40  
  7 purchase totals = $839.37       $911.2798   $911.28   $911.30   $911.30