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	$79.53	13.542%	$90.3	$90.30	$90.30	$90.30
Purchase #2	$141.67	11.872%	$158.4891	$158.49	$158.50	$158.50
Purchase #3	$175.94	9.303%	$192.3077	$192.31	$192.30	$192.30
Purchase #4	$121.46	5.440%	$128.0674	$128.07	$128.05	$128.10
Purchase #5	$37.46	4.262%	$39.0565	$39.06	$39.05	$39.10
Purchase #6	$161.64	13.862%	$184.0465	$184.05	$184.05	$184.00
Purchase #7	$17.42	5.125%	$18.3128	$18.31	$18.30	$18.30
7 purchase totals =	$735.12		$810.5800	$810.59	$810.55	$810.60