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	$173.56	3.670%	$179.9297	$179.93	$179.95	$179.90
Purchase #2	$43.90	5.168%	$46.1688	$46.17	$46.15	$46.20
Purchase #3	$89.25	9.156%	$97.4217	$97.42	$97.40	$97.40
Purchase #4	$16.91	12.671%	$19.0527	$19.05	$19.05	$19.10
Purchase #5	$86.76	3.764%	$90.0256	$90.03	$90.05	$90.00
Purchase #6	$117.37	10.847%	$130.1011	$130.10	$130.10	$130.10
Purchase #7	$8.97	12.314%	$10.0746	$10.07	$10.05	$10.10
7 purchase totals =	$536.72		$572.7742	$572.77	$572.75	$572.80