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	$171.96	7.816%	$185.4004	$185.40	$185.40	$185.40
Purchase #2	$178.66	11.787%	$199.7187	$199.72	$199.70	$199.70
Purchase #3	$250.45	13.449%	$284.133	$284.13	$284.15	$284.10
Purchase #4	$118.76	3.643%	$123.0864	$123.09	$123.10	$123.10
Purchase #5	$100.30	8.726%	$109.0522	$109.05	$109.05	$109.10
Purchase #6	$100.40	7.708%	$108.1388	$108.14	$108.15	$108.10
Purchase #7	$17.61	6.611%	$18.7742	$18.77	$18.75	$18.80
7 purchase totals =	$938.14		$1,028.3037	$1,028.30	$1,028.30	$1,028.30