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	$45.67	11.701%	$51.0138	$51.01	$51.00	$51.00
Purchase #2	$113.31	12.371%	$127.3276	$127.33	$127.35	$127.30
Purchase #3	$183.91	3.574%	$190.4829	$190.48	$190.50	$190.50
Purchase #4	$158.31	3.595%	$164.0012	$164.00	$164.00	$164.00
Purchase #5	$211.78	13.324%	$239.9976	$240.00	$240.00	$240.00
Purchase #6	$10.59	8.126%	$11.4505	$11.45	$11.45	$11.50
Purchase #7	$195.26	9.672%	$214.1455	$214.15	$214.15	$214.10
7 purchase totals =	$918.83		$998.4191	$998.42	$998.45	$998.40