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	$239.39	4.358%	$249.8226	$249.82	$249.80	$249.80
Purchase #2	$92.88	8.600%	$100.8677	$100.87	$100.85	$100.90
Purchase #3	$62.32	6.481%	$66.359	$66.36	$66.35	$66.40
Purchase #4	$30.36	13.685%	$34.5148	$34.51	$34.50	$34.50
Purchase #5	$136.51	7.244%	$146.3988	$146.40	$146.40	$146.40
Purchase #6	$67.52	3.807%	$70.0905	$70.09	$70.10	$70.10
Purchase #7	$18.69	7.474%	$20.0869	$20.09	$20.10	$20.10
7 purchase totals =	$647.67		$688.1403	$688.14	$688.10	$688.20