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	$139.68	13.474%	$158.5005	$158.50	$158.50	$158.50
Purchase #2	$89.75	6.720%	$95.7812	$95.78	$95.80	$95.80
Purchase #3	$174.72	9.496%	$191.3114	$191.31	$191.30	$191.30
Purchase #4	$16.50	3.457%	$17.0704	$17.07	$17.05	$17.10
Purchase #5	$183.26	6.112%	$194.4609	$194.46	$194.45	$194.50
Purchase #6	$223.32	6.731%	$238.3517	$238.35	$238.35	$238.40
Purchase #7	$53.78	4.321%	$56.1038	$56.10	$56.10	$56.10
7 purchase totals =	$881.01		$951.5799	$951.57	$951.55	$951.70