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	$56.65	5.463%	$59.7448	$59.74	$59.75	$59.70
Purchase #2	$235.97	12.162%	$264.6687	$264.67	$264.65	$264.70
Purchase #3	$75.77	13.357%	$85.8906	$85.89	$85.90	$85.90
Purchase #4	$122.83	11.827%	$137.3571	$137.36	$137.35	$137.40
Purchase #5	$14.26	6.832%	$15.2342	$15.23	$15.25	$15.20
Purchase #6	$10.95	10.769%	$12.1292	$12.13	$12.15	$12.10
Purchase #7	$159.59	12.414%	$179.4015	$179.40	$179.40	$179.40
7 purchase totals =	$676.02		$754.4261	$754.42	$754.45	$754.40