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	$79.81	7.154%	$85.5196	$85.52	$85.50	$85.50
Purchase #2	$190.44	11.597%	$212.5253	$212.53	$212.55	$212.50
Purchase #3	$158.63	8.601%	$172.2738	$172.27	$172.25	$172.30
Purchase #4	$76.82	5.200%	$80.8146	$80.81	$80.80	$80.80
Purchase #5	$62.67	6.384%	$66.6709	$66.67	$66.65	$66.70
Purchase #6	$204.72	3.387%	$211.6539	$211.65	$211.65	$211.70
Purchase #7	$238.58	8.857%	$259.711	$259.71	$259.70	$259.70
7 purchase totals =	$1,011.67		$1,089.1691	$1,089.16	$1,089.10	$1,089.20