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	$118.72	4.806%	$124.4257	$124.43	$124.45	$124.40
Purchase #2	$162.65	7.650%	$175.0927	$175.09	$175.10	$175.10
Purchase #3	$60.86	9.665%	$66.7421	$66.74	$66.75	$66.70
Purchase #4	$56.44	8.298%	$61.1234	$61.12	$61.10	$61.10
Purchase #5	$5.25	10.780%	$5.816	$5.82	$5.80	$5.80
Purchase #6	$85.66	4.804%	$89.7751	$89.78	$89.80	$89.80
Purchase #7	$32.56	4.466%	$34.0141	$34.01	$34.00	$34.00
7 purchase totals =	$522.14		$556.9891	$556.99	$557.00	$556.90