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	$167.72	7.175%	$179.7539	$179.75	$179.75	$179.80
Purchase #2	$104.80	4.635%	$109.6575	$109.66	$109.65	$109.70
Purchase #3	$124.76	10.830%	$138.2715	$138.27	$138.25	$138.30
Purchase #4	$180.86	6.153%	$191.9883	$191.99	$192.00	$192.00
Purchase #5	$61.94	13.538%	$70.3254	$70.33	$70.35	$70.30
Purchase #6	$223.45	10.828%	$247.6452	$247.65	$247.65	$247.60
Purchase #7	$54.49	9.215%	$59.5113	$59.51	$59.50	$59.50
7 purchase totals =	$918.02		$997.1531	$997.16	$997.15	$997.20