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 $199.36   4.567%   $208.4648   $208.46   $208.45   $208.50  
  Purchase #2 $192.64   13.607%   $218.8525   $218.85   $218.85   $218.90  
  Purchase #3 $13.66   12.123%   $15.316   $15.32   $15.30   $15.30  
  Purchase #4 $134.41   5.788%   $142.1897   $142.19   $142.20   $142.20  
  Purchase #5 $93.82   13.603%   $106.5823   $106.58   $106.60   $106.60  
  Purchase #6 $208.44   9.675%   $228.6066   $228.61   $228.60   $228.60  
  Purchase #7 $125.31   3.140%   $129.2447   $129.24   $129.25   $129.20  
  7 purchase totals = $967.64       $1,049.2566   $1,049.25   $1,049.25   $1,049.30