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 $202.36   6.177%   $214.8598   $214.86   $214.85   $214.90  
  Purchase #2 $6.51   11.471%   $7.2568   $7.26   $7.25   $7.30  
  Purchase #3 $155.44   8.311%   $168.3586   $168.36   $168.35   $168.40  
  Purchase #4 $59.61   4.603%   $62.3538   $62.35   $62.35   $62.40  
  Purchase #5 $145.98   12.622%   $164.4056   $164.41   $164.40   $164.40  
  Purchase #6 $88.36   9.708%   $96.938   $96.94   $96.95   $96.90  
  Purchase #7 $124.66   4.493%   $130.261   $130.26   $130.25   $130.30  
  7 purchase totals = $782.92       $844.4336   $844.44   $844.40   $844.60