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	$38.37	4.856%	$40.2332	$40.23	$40.25	$40.20
Purchase #2	$159.72	9.129%	$174.3008	$174.30	$174.30	$174.30
Purchase #3	$146.94	3.837%	$152.5781	$152.58	$152.60	$152.60
Purchase #4	$110.37	6.773%	$117.8454	$117.85	$117.85	$117.80
Purchase #5	$142.91	7.257%	$153.281	$153.28	$153.30	$153.30
Purchase #6	$153.96	7.549%	$165.5824	$165.58	$165.60	$165.60
Purchase #7	$150.26	11.236%	$167.1432	$167.14	$167.15	$167.10
7 purchase totals =	$902.53		$970.9641	$970.96	$971.05	$970.90