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	$73.39	6.852%	$78.4187	$78.42	$78.40	$78.40
Purchase #2	$33.38	3.167%	$34.4371	$34.44	$34.45	$34.40
Purchase #3	$13.34	4.856%	$13.9878	$13.99	$14.00	$14.00
Purchase #4	$52.57	9.471%	$57.5489	$57.55	$57.55	$57.50
Purchase #5	$141.63	11.759%	$158.2843	$158.28	$158.30	$158.30
Purchase #6	$7.92	12.567%	$8.9153	$8.92	$8.90	$8.90
Purchase #7	$170.29	10.722%	$188.5485	$188.55	$188.55	$188.50
7 purchase totals =	$492.52		$540.1406	$540.15	$540.15	$540.00