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	$17.27	4.319%	$18.0159	$18.02	$18.00	$18.00
Purchase #2	$151.25	13.361%	$171.4585	$171.46	$171.45	$171.50
Purchase #3	$79.69	13.602%	$90.5294	$90.53	$90.55	$90.50
Purchase #4	$31.98	5.356%	$33.6928	$33.69	$33.70	$33.70
Purchase #5	$73.29	5.371%	$77.2264	$77.23	$77.25	$77.20
Purchase #6	$239.38	5.572%	$252.7183	$252.72	$252.70	$252.70
Purchase #7	$156.72	10.760%	$173.5831	$173.58	$173.60	$173.60
7 purchase totals =	$749.58		$817.2244	$817.23	$817.25	$817.20