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	$250.29	13.559%	$284.2268	$284.23	$284.25	$284.20
Purchase #2	$84.37	13.714%	$95.9405	$95.94	$95.95	$95.90
Purchase #3	$65.95	7.339%	$70.7901	$70.79	$70.80	$70.80
Purchase #4	$49.52	5.717%	$52.3511	$52.35	$52.35	$52.40
Purchase #5	$64.80	11.468%	$72.2313	$72.23	$72.25	$72.20
Purchase #6	$64.83	11.240%	$72.1169	$72.12	$72.10	$72.10
Purchase #7	$107.25	9.107%	$117.0173	$117.02	$117.00	$117.00
7 purchase totals =	$687.01		$764.6740	$764.68	$764.70	$764.60