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	$73.78	13.260%	$83.5632	$83.56	$83.55	$83.60
Purchase #2	$68.49	13.766%	$77.9183	$77.92	$77.90	$77.90
Purchase #3	$36.50	10.776%	$40.4332	$40.43	$40.45	$40.40
Purchase #4	$19.59	13.305%	$22.1964	$22.20	$22.20	$22.20
Purchase #5	$59.79	10.607%	$66.1319	$66.13	$66.15	$66.10
Purchase #6	$79.70	13.189%	$90.2116	$90.21	$90.20	$90.20
Purchase #7	$224.90	11.829%	$251.5034	$251.50	$251.50	$251.50
7 purchase totals =	$562.75		$631.9580	$631.95	$631.95	$631.90