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	$94.92	10.802%	$105.1733	$105.17	$105.15	$105.20
Purchase #2	$75.38	7.317%	$80.8956	$80.90	$80.90	$80.90
Purchase #3	$103.36	7.495%	$111.1068	$111.11	$111.10	$111.10
Purchase #4	$15.94	9.542%	$17.461	$17.46	$17.45	$17.50
Purchase #5	$96.81	6.683%	$103.2798	$103.28	$103.30	$103.30
Purchase #6	$51.58	13.289%	$58.4345	$58.43	$58.45	$58.40
Purchase #7	$69.34	11.287%	$77.1664	$77.17	$77.15	$77.20
7 purchase totals =	$507.33		$553.5174	$553.52	$553.50	$553.60