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	$235.49	8.254%	$254.9273	$254.93	$254.95	$254.90
Purchase #2	$172.91	10.395%	$190.884	$190.88	$190.90	$190.90
Purchase #3	$58.62	3.693%	$60.7848	$60.78	$60.80	$60.80
Purchase #4	$161.79	5.267%	$170.3115	$170.31	$170.30	$170.30
Purchase #5	$150.88	7.703%	$162.5023	$162.50	$162.50	$162.50
Purchase #6	$70.78	13.182%	$80.1102	$80.11	$80.10	$80.10
Purchase #7	$214.29	3.841%	$222.5209	$222.52	$222.50	$222.50
7 purchase totals =	$1,064.76		$1,142.0410	$1,142.03	$1,142.05	$1,142.00