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	$101.92	9.759%	$111.8664	$111.87	$111.85	$111.90
Purchase #2	$216.33	12.129%	$242.5687	$242.57	$242.55	$242.60
Purchase #3	$236.60	13.751%	$269.1349	$269.13	$269.15	$269.10
Purchase #4	$43.73	11.535%	$48.7743	$48.77	$48.75	$48.80
Purchase #5	$99.80	9.420%	$109.2012	$109.20	$109.20	$109.20
Purchase #6	$28.72	3.696%	$29.7815	$29.78	$29.80	$29.80
Purchase #7	$29.82	10.543%	$32.9639	$32.96	$32.95	$33.00
7 purchase totals =	$756.92		$844.2909	$844.28	$844.25	$844.40