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	$14.63	6.179%	$15.534	$15.53	$15.55	$15.50
Purchase #2	$20.61	4.248%	$21.4855	$21.49	$21.50	$21.50
Purchase #3	$176.73	6.470%	$188.1644	$188.16	$188.15	$188.20
Purchase #4	$37.60	4.823%	$39.4134	$39.41	$39.40	$39.40
Purchase #5	$11.64	3.865%	$12.0899	$12.09	$12.10	$12.10
Purchase #6	$136.74	7.627%	$147.1692	$147.17	$147.15	$147.20
Purchase #7	$207.37	4.665%	$217.0438	$217.04	$217.05	$217.00
7 purchase totals =	$605.32		$640.9002	$640.89	$640.90	$640.90