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	$42.55	13.790%	$48.4176	$48.42	$48.40	$48.40
Purchase #2	$140.28	10.519%	$155.0361	$155.04	$155.05	$155.00
Purchase #3	$203.76	13.245%	$230.748	$230.75	$230.75	$230.70
Purchase #4	$228.32	7.187%	$244.7294	$244.73	$244.75	$244.70
Purchase #5	$105.73	5.765%	$111.8253	$111.83	$111.85	$111.80
Purchase #6	$84.36	7.678%	$90.8372	$90.84	$90.85	$90.80
Purchase #7	$80.28	9.404%	$87.8295	$87.83	$87.85	$87.80
7 purchase totals =	$885.28		$969.4231	$969.44	$969.50	$969.20