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	$216.89	13.604%	$246.3957	$246.40	$246.40	$246.40
Purchase #2	$48.85	6.812%	$52.1777	$52.18	$52.20	$52.20
Purchase #3	$132.98	13.834%	$151.3765	$151.38	$151.40	$151.40
Purchase #4	$8.31	6.433%	$8.8446	$8.84	$8.85	$8.80
Purchase #5	$220.28	4.466%	$230.1177	$230.12	$230.10	$230.10
Purchase #6	$52.97	13.104%	$59.9112	$59.91	$59.90	$59.90
Purchase #7	$103.63	5.480%	$109.3089	$109.31	$109.30	$109.30
7 purchase totals =	$783.91		$858.1323	$858.14	$858.15	$858.10