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	$248.78	10.702%	$275.4044	$275.40	$275.40	$275.40
Purchase #2	$123.49	4.838%	$129.4644	$129.46	$129.45	$129.50
Purchase #3	$67.55	7.365%	$72.5251	$72.53	$72.55	$72.50
Purchase #4	$59.89	10.679%	$66.2857	$66.29	$66.30	$66.30
Purchase #5	$222.51	5.589%	$234.9461	$234.95	$234.95	$234.90
Purchase #6	$47.51	13.117%	$53.7419	$53.74	$53.75	$53.70
Purchase #7	$45.87	12.550%	$51.6267	$51.63	$51.65	$51.60
7 purchase totals =	$815.60		$883.9943	$884.00	$884.05	$883.90