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	$74.38	12.448%	$83.6388	$83.64	$83.65	$83.60
Purchase #2	$96.63	13.203%	$109.3881	$109.39	$109.40	$109.40
Purchase #3	$110.50	6.584%	$117.7753	$117.78	$117.80	$117.80
Purchase #4	$45.82	8.124%	$49.5424	$49.54	$49.55	$49.50
Purchase #5	$214.77	10.112%	$236.4875	$236.49	$236.50	$236.50
Purchase #6	$172.52	13.610%	$196	$196.00	$196.00	$196.00
Purchase #7	$72.73	6.376%	$77.3673	$77.37	$77.35	$77.40
7 purchase totals =	$787.35		$870.1994	$870.21	$870.25	$870.20