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	$87.57	13.116%	$99.0557	$99.06	$99.05	$99.10
Purchase #2	$162.96	7.506%	$175.1918	$175.19	$175.20	$175.20
Purchase #3	$208.35	5.233%	$219.253	$219.25	$219.25	$219.30
Purchase #4	$119.43	9.603%	$130.8989	$130.90	$130.90	$130.90
Purchase #5	$47.92	13.490%	$54.3844	$54.38	$54.40	$54.40
Purchase #6	$122.36	7.122%	$131.0745	$131.07	$131.05	$131.10
Purchase #7	$56.66	6.385%	$60.2777	$60.28	$60.30	$60.30
7 purchase totals =	$805.25		$870.1360	$870.13	$870.15	$870.30