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	$56.49	5.107%	$59.3749	$59.37	$59.35	$59.40
Purchase #2	$112.51	9.685%	$123.4066	$123.41	$123.40	$123.40
Purchase #3	$25.70	5.486%	$27.1099	$27.11	$27.10	$27.10
Purchase #4	$22.61	10.572%	$25.0003	$25.00	$25.00	$25.00
Purchase #5	$154.51	7.307%	$165.8	$165.80	$165.80	$165.80
Purchase #6	$108.85	6.843%	$116.2986	$116.30	$116.30	$116.30
Purchase #7	$159.34	10.860%	$176.6443	$176.64	$176.65	$176.60
7 purchase totals =	$640.01		$693.6346	$693.63	$693.60	$693.60