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	$91.88	12.521%	$103.3843	$103.38	$103.40	$103.40
Purchase #2	$215.66	11.388%	$240.2194	$240.22	$240.20	$240.20
Purchase #3	$25.56	9.644%	$28.025	$28.03	$28.05	$28.00
Purchase #4	$52.95	13.634%	$60.1692	$60.17	$60.15	$60.20
Purchase #5	$51.48	3.239%	$53.1474	$53.15	$53.15	$53.10
Purchase #6	$171.66	12.195%	$192.5939	$192.59	$192.60	$192.60
Purchase #7	$104.61	6.488%	$111.3971	$111.40	$111.40	$111.40
7 purchase totals =	$713.80		$788.9363	$788.94	$788.95	$788.90