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	$5.87	9.258%	$6.4134	$6.41	$6.40	$6.40
Purchase #2	$224.48	13.633%	$255.0834	$255.08	$255.10	$255.10
Purchase #3	$204.72	6.599%	$218.2295	$218.23	$218.25	$218.20
Purchase #4	$143.83	11.685%	$160.6365	$160.64	$160.65	$160.60
Purchase #5	$159.77	13.761%	$181.7559	$181.76	$181.75	$181.80
Purchase #6	$65.42	9.109%	$71.3791	$71.38	$71.40	$71.40
Purchase #7	$37.52	4.758%	$39.3052	$39.31	$39.30	$39.30
7 purchase totals =	$841.61		$932.8030	$932.81	$932.85	$932.80