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	$18.69	10.174%	$20.5915	$20.59	$20.60	$20.60
Purchase #2	$206.31	8.446%	$223.7349	$223.73	$223.75	$223.70
Purchase #3	$79.64	13.511%	$90.4002	$90.40	$90.40	$90.40
Purchase #4	$21.79	5.190%	$22.9209	$22.92	$22.90	$22.90
Purchase #5	$89.26	4.677%	$93.4347	$93.43	$93.45	$93.40
Purchase #6	$5.70	8.316%	$6.174	$6.17	$6.15	$6.20
Purchase #7	$238.30	7.128%	$255.286	$255.29	$255.30	$255.30
7 purchase totals =	$659.69		$712.5422	$712.53	$712.55	$712.50