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	$149.28	12.722%	$168.2714	$168.27	$168.25	$168.30
Purchase #2	$166.45	3.792%	$172.7618	$172.76	$172.75	$172.80
Purchase #3	$71.58	4.503%	$74.8032	$74.80	$74.80	$74.80
Purchase #4	$32.49	10.586%	$35.9294	$35.93	$35.95	$35.90
Purchase #5	$181.90	4.191%	$189.5234	$189.52	$189.50	$189.50
Purchase #6	$133.55	9.777%	$146.6072	$146.61	$146.60	$146.60
Purchase #7	$235.77	11.436%	$262.7327	$262.73	$262.75	$262.70
7 purchase totals =	$971.02		$1,050.6291	$1,050.62	$1,050.60	$1,050.60