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	$151.66	9.871%	$166.6304	$166.63	$166.65	$166.60
Purchase #2	$216.26	12.634%	$243.5823	$243.58	$243.60	$243.60
Purchase #3	$160.72	6.801%	$171.6506	$171.65	$171.65	$171.70
Purchase #4	$88.32	12.407%	$99.2779	$99.28	$99.30	$99.30
Purchase #5	$132.33	13.525%	$150.2276	$150.23	$150.25	$150.20
Purchase #6	$11.29	9.831%	$12.3999	$12.40	$12.40	$12.40
Purchase #7	$117.79	8.585%	$127.9023	$127.90	$127.90	$127.90
7 purchase totals =	$878.37		$971.6710	$971.67	$971.75	$971.70