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 $108.71   6.562%   $115.8436   $115.84   $115.85   $115.80  
  Purchase #2 $56.96   4.303%   $59.411   $59.41   $59.40   $59.40  
  Purchase #3 $8.74   7.176%   $9.3672   $9.37   $9.35   $9.40  
  Purchase #4 $147.42   11.138%   $163.8396   $163.84   $163.85   $163.80  
  Purchase #5 $177.49   4.513%   $185.5001   $185.50   $185.50   $185.50  
  Purchase #6 $164.86   11.560%   $183.9178   $183.92   $183.90   $183.90  
  Purchase #7 $178.45   13.198%   $202.0018   $202.00   $202.00   $202.00  
  7 purchase totals = $842.63       $919.8811   $919.88   $919.85   $919.80