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	$129.77	9.787%	$142.4706	$142.47	$142.45	$142.50
Purchase #2	$245.49	6.834%	$262.2668	$262.27	$262.25	$262.30
Purchase #3	$248.77	6.363%	$264.5992	$264.60	$264.60	$264.60
Purchase #4	$141.32	8.748%	$153.6827	$153.68	$153.70	$153.70
Purchase #5	$131.85	9.335%	$144.1582	$144.16	$144.15	$144.20
Purchase #6	$151.55	4.729%	$158.7168	$158.72	$158.70	$158.70
Purchase #7	$72.89	6.834%	$77.8713	$77.87	$77.85	$77.90
7 purchase totals =	$1,121.64		$1,203.7656	$1,203.77	$1,203.70	$1,203.90