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	$158.87	4.171%	$165.4965	$165.50	$165.50	$165.50
Purchase #2	$199.77	13.265%	$226.2695	$226.27	$226.25	$226.30
Purchase #3	$239.66	3.372%	$247.7413	$247.74	$247.75	$247.70
Purchase #4	$101.97	6.483%	$108.5807	$108.58	$108.60	$108.60
Purchase #5	$97.43	12.670%	$109.7744	$109.77	$109.75	$109.80
Purchase #6	$70.29	11.689%	$78.5062	$78.51	$78.50	$78.50
Purchase #7	$238.74	10.333%	$263.409	$263.41	$263.40	$263.40
7 purchase totals =	$1,106.73		$1,199.7776	$1,199.78	$1,199.75	$1,199.80