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 $204.91   13.792%   $233.1712   $233.17   $233.15   $233.20  
  Purchase #2 $127.39   5.167%   $133.9722   $133.97   $133.95   $134.00  
  Purchase #3 $207.89   6.712%   $221.8436   $221.84   $221.85   $221.80  
  Purchase #4 $222.40   11.591%   $248.1784   $248.18   $248.20   $248.20  
  Purchase #5 $179.27   12.312%   $201.3417   $201.34   $201.35   $201.30  
  Purchase #6 $182.40   9.322%   $199.4033   $199.40   $199.40   $199.40  
  Purchase #7 $241.59   7.139%   $258.8371   $258.84   $258.85   $258.80  
  7 purchase totals = $1,365.85       $1,496.7475   $1,496.74   $1,496.75   $1,496.70