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	$75.48	8.861%	$82.1683	$82.17	$82.15	$82.20
Purchase #2	$173.95	9.620%	$190.684	$190.68	$190.70	$190.70
Purchase #3	$80.31	11.308%	$89.3915	$89.39	$89.40	$89.40
Purchase #4	$195.72	5.785%	$207.0424	$207.04	$207.05	$207.00
Purchase #5	$185.93	4.241%	$193.8153	$193.82	$193.80	$193.80
Purchase #6	$41.45	10.445%	$45.7795	$45.78	$45.80	$45.80
Purchase #7	$228.91	4.266%	$238.6753	$238.68	$238.70	$238.70
7 purchase totals =	$981.75		$1,047.5563	$1,047.56	$1,047.60	$1,047.60