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	$54.28	4.394%	$56.6651	$56.67	$56.65	$56.70
Purchase #2	$223.37	12.179%	$250.5742	$250.57	$250.55	$250.60
Purchase #3	$101.87	3.692%	$105.631	$105.63	$105.65	$105.60
Purchase #4	$20.29	7.617%	$21.8355	$21.84	$21.85	$21.80
Purchase #5	$92.56	9.297%	$101.1653	$101.17	$101.15	$101.20
Purchase #6	$244.45	12.785%	$275.7029	$275.70	$275.70	$275.70
Purchase #7	$131.77	13.848%	$150.0175	$150.02	$150.00	$150.00
7 purchase totals =	$868.59		$961.5915	$961.60	$961.55	$961.60