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	$19.74	5.241%	$20.7746	$20.77	$20.75	$20.80
Purchase #2	$230.35	11.497%	$256.8333	$256.83	$256.85	$256.80
Purchase #3	$66.72	10.109%	$73.4647	$73.46	$73.45	$73.50
Purchase #4	$237.51	7.167%	$254.5323	$254.53	$254.55	$254.50
Purchase #5	$168.45	11.668%	$188.1047	$188.10	$188.10	$188.10
Purchase #6	$9.51	12.116%	$10.6622	$10.66	$10.65	$10.70
Purchase #7	$236.81	9.177%	$258.5421	$258.54	$258.55	$258.50
7 purchase totals =	$969.09		$1,062.9139	$1,062.89	$1,062.90	$1,062.90