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	$77.36	6.542%	$82.4209	$82.42	$82.40	$82.40
Purchase #2	$89.56	11.803%	$100.1308	$100.13	$100.15	$100.10
Purchase #3	$60.61	9.736%	$66.511	$66.51	$66.50	$66.50
Purchase #4	$250.88	3.581%	$259.864	$259.86	$259.85	$259.90
Purchase #5	$26.80	6.553%	$28.5562	$28.56	$28.55	$28.60
Purchase #6	$131.61	6.123%	$139.6685	$139.67	$139.65	$139.70
Purchase #7	$210.36	10.647%	$232.757	$232.76	$232.75	$232.80
7 purchase totals =	$847.18		$909.9084	$909.91	$909.85	$910.00