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	$19.59	8.540%	$21.263	$21.26	$21.25	$21.30
Purchase #2	$225.47	13.156%	$255.1328	$255.13	$255.15	$255.10
Purchase #3	$32.96	10.401%	$36.3882	$36.39	$36.40	$36.40
Purchase #4	$58.45	3.663%	$60.591	$60.59	$60.60	$60.60
Purchase #5	$18.26	11.824%	$20.4191	$20.42	$20.40	$20.40
Purchase #6	$121.43	8.106%	$131.2731	$131.27	$131.25	$131.30
Purchase #7	$98.43	6.841%	$105.1636	$105.16	$105.15	$105.20
7 purchase totals =	$574.59		$630.2308	$630.22	$630.20	$630.30