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	$150.53	8.141%	$162.7846	$162.78	$162.80	$162.80
Purchase #2	$132.88	10.567%	$146.9214	$146.92	$146.90	$146.90
Purchase #3	$55.96	8.530%	$60.7334	$60.73	$60.75	$60.70
Purchase #4	$10.80	10.442%	$11.9277	$11.93	$11.95	$11.90
Purchase #5	$233.52	6.212%	$248.0263	$248.03	$248.05	$248.00
Purchase #6	$82.27	9.489%	$90.0766	$90.08	$90.10	$90.10
Purchase #7	$152.76	3.704%	$158.4182	$158.42	$158.40	$158.40
7 purchase totals =	$818.72		$878.8882	$878.89	$878.95	$878.80