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	$24.25	5.575%	$25.6019	$25.60	$25.60	$25.60
Purchase #2	$134.84	9.244%	$147.3046	$147.30	$147.30	$147.30
Purchase #3	$56.74	8.439%	$61.5283	$61.53	$61.55	$61.50
Purchase #4	$49.63	3.231%	$51.2335	$51.23	$51.25	$51.20
Purchase #5	$111.78	10.869%	$123.9294	$123.93	$123.95	$123.90
Purchase #6	$48.54	12.813%	$54.7594	$54.76	$54.75	$54.80
Purchase #7	$78.93	3.281%	$81.5197	$81.52	$81.50	$81.50
7 purchase totals =	$504.71		$545.8768	$545.87	$545.90	$545.80