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	$32.49	5.482%	$34.2711	$34.27	$34.25	$34.30
Purchase #2	$43.68	13.551%	$49.5991	$49.60	$49.60	$49.60
Purchase #3	$100.25	12.592%	$112.8735	$112.87	$112.85	$112.90
Purchase #4	$247.42	11.463%	$275.7818	$275.78	$275.80	$275.80
Purchase #5	$154.64	10.109%	$170.2726	$170.27	$170.25	$170.30
Purchase #6	$191.33	12.512%	$215.2692	$215.27	$215.25	$215.30
Purchase #7	$210.46	9.132%	$229.6792	$229.68	$229.70	$229.70
7 purchase totals =	$980.27		$1,087.7465	$1,087.74	$1,087.70	$1,087.90