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	$150.26	6.596%	$160.1711	$160.17	$160.15	$160.20
Purchase #2	$106.35	4.553%	$111.1921	$111.19	$111.20	$111.20
Purchase #3	$93.85	7.732%	$101.1065	$101.11	$101.10	$101.10
Purchase #4	$62.86	5.370%	$66.2356	$66.24	$66.25	$66.20
Purchase #5	$112.96	12.714%	$127.3217	$127.32	$127.30	$127.30
Purchase #6	$227.25	10.852%	$251.9112	$251.91	$251.90	$251.90
Purchase #7	$204.80	9.785%	$224.8397	$224.84	$224.85	$224.80
7 purchase totals =	$958.33		$1,042.7779	$1,042.78	$1,042.75	$1,042.70