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	$66.30	12.403%	$74.5232	$74.52	$74.50	$74.50
Purchase #2	$175.46	8.601%	$190.5513	$190.55	$190.55	$190.60
Purchase #3	$98.68	4.116%	$102.7417	$102.74	$102.75	$102.70
Purchase #4	$120.44	5.132%	$126.621	$126.62	$126.60	$126.60
Purchase #5	$79.89	7.483%	$85.8682	$85.87	$85.85	$85.90
Purchase #6	$82.67	8.762%	$89.9135	$89.91	$89.90	$89.90
Purchase #7	$233.77	10.854%	$259.1434	$259.14	$259.15	$259.10
7 purchase totals =	$857.21		$929.3623	$929.35	$929.30	$929.30