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	$79.41	7.137%	$85.0775	$85.08	$85.10	$85.10
Purchase #2	$73.56	13.801%	$83.712	$83.71	$83.70	$83.70
Purchase #3	$99.88	11.327%	$111.1934	$111.19	$111.20	$111.20
Purchase #4	$30.70	5.601%	$32.4195	$32.42	$32.40	$32.40
Purchase #5	$27.62	10.271%	$30.4569	$30.46	$30.45	$30.50
Purchase #6	$164.61	10.407%	$181.741	$181.74	$181.75	$181.70
Purchase #7	$50.94	5.321%	$53.6505	$53.65	$53.65	$53.70
7 purchase totals =	$526.72		$578.2508	$578.25	$578.25	$578.30