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	$27.39	5.572%	$28.9162	$28.92	$28.90	$28.90
Purchase #2	$42.45	9.871%	$46.6402	$46.64	$46.65	$46.60
Purchase #3	$53.59	11.601%	$59.807	$59.81	$59.80	$59.80
Purchase #4	$20.31	8.786%	$22.0944	$22.09	$22.10	$22.10
Purchase #5	$55.52	9.464%	$60.7744	$60.77	$60.75	$60.80
Purchase #6	$216.51	13.180%	$245.046	$245.05	$245.05	$245.00
Purchase #7	$153.40	3.564%	$158.8672	$158.87	$158.85	$158.90
7 purchase totals =	$569.17		$622.1454	$622.15	$622.10	$622.10