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	$46.47	9.842%	$51.0436	$51.04	$51.05	$51.00
Purchase #2	$6.32	6.685%	$6.7425	$6.74	$6.75	$6.70
Purchase #3	$50.35	9.430%	$55.098	$55.10	$55.10	$55.10
Purchase #4	$129.77	5.615%	$137.0566	$137.06	$137.05	$137.10
Purchase #5	$173.65	3.604%	$179.9083	$179.91	$179.90	$179.90
Purchase #6	$102.30	9.130%	$111.64	$111.64	$111.65	$111.60
Purchase #7	$50.60	7.173%	$54.2295	$54.23	$54.25	$54.20
7 purchase totals =	$559.46		$595.7185	$595.72	$595.75	$595.60