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	$103.88	7.578%	$111.752	$111.75	$111.75	$111.80
Purchase #2	$215.87	5.549%	$227.8486	$227.85	$227.85	$227.80
Purchase #3	$213.70	5.634%	$225.7399	$225.74	$225.75	$225.70
Purchase #4	$118.96	10.357%	$131.2807	$131.28	$131.30	$131.30
Purchase #5	$68.71	12.766%	$77.4815	$77.48	$77.50	$77.50
Purchase #6	$22.64	4.624%	$23.6869	$23.69	$23.70	$23.70
Purchase #7	$52.42	13.461%	$59.4763	$59.48	$59.50	$59.50
7 purchase totals =	$796.18		$857.2659	$857.27	$857.35	$857.30