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	$156.82	5.851%	$165.9955	$166.00	$166.00	$166.00
Purchase #2	$141.50	6.844%	$151.1843	$151.18	$151.20	$151.20
Purchase #3	$58.26	12.339%	$65.4487	$65.45	$65.45	$65.40
Purchase #4	$98.49	13.355%	$111.6433	$111.64	$111.65	$111.60
Purchase #5	$191.32	11.130%	$212.6139	$212.61	$212.60	$212.60
Purchase #6	$222.60	5.579%	$235.0189	$235.02	$235.00	$235.00
Purchase #7	$127.70	9.539%	$139.8813	$139.88	$139.90	$139.90
7 purchase totals =	$996.69		$1,081.7859	$1,081.78	$1,081.80	$1,081.70