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	$40.62	3.712%	$42.1278	$42.13	$42.15	$42.10
Purchase #2	$225.49	13.633%	$256.2311	$256.23	$256.25	$256.20
Purchase #3	$121.67	7.797%	$131.1566	$131.16	$131.15	$131.20
Purchase #4	$130.33	11.776%	$145.6777	$145.68	$145.70	$145.70
Purchase #5	$138.41	5.370%	$145.8426	$145.84	$145.85	$145.80
Purchase #6	$219.37	13.451%	$248.8775	$248.88	$248.90	$248.90
Purchase #7	$103.59	4.222%	$107.9636	$107.96	$107.95	$108.00
7 purchase totals =	$979.48		$1,077.8769	$1,077.88	$1,077.95	$1,077.90