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	$166.30	4.554%	$173.8733	$173.87	$173.85	$173.90
Purchase #2	$72.65	11.134%	$80.7389	$80.74	$80.75	$80.70
Purchase #3	$145.65	7.323%	$156.3159	$156.32	$156.30	$156.30
Purchase #4	$127.91	6.330%	$136.0067	$136.01	$136.00	$136.00
Purchase #5	$12.61	9.322%	$13.7855	$13.79	$13.80	$13.80
Purchase #6	$66.30	9.433%	$72.5541	$72.55	$72.55	$72.60
Purchase #7	$127.26	9.568%	$139.4362	$139.44	$139.45	$139.40
7 purchase totals =	$718.68		$772.7106	$772.72	$772.70	$772.70