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	$20.50	3.267%	$21.1697	$21.17	$21.15	$21.20
Purchase #2	$15.65	13.629%	$17.7829	$17.78	$17.80	$17.80
Purchase #3	$223.56	13.384%	$253.4813	$253.48	$253.50	$253.50
Purchase #4	$185.34	4.383%	$193.4635	$193.46	$193.45	$193.50
Purchase #5	$178.89	6.519%	$190.5518	$190.55	$190.55	$190.60
Purchase #6	$158.92	7.785%	$171.2919	$171.29	$171.30	$171.30
Purchase #7	$151.54	4.481%	$158.3305	$158.33	$158.35	$158.30
7 purchase totals =	$934.40		$1,006.0716	$1,006.06	$1,006.10	$1,006.20