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	$81.80	12.618%	$92.1215	$92.12	$92.10	$92.10
Purchase #2	$47.57	11.746%	$53.1576	$53.16	$53.15	$53.20
Purchase #3	$70.38	10.850%	$78.0162	$78.02	$78.00	$78.00
Purchase #4	$41.99	4.553%	$43.9018	$43.90	$43.90	$43.90
Purchase #5	$128.95	10.449%	$142.424	$142.42	$142.40	$142.40
Purchase #6	$50.35	8.286%	$54.522	$54.52	$54.50	$54.50
Purchase #7	$93.90	13.531%	$106.6056	$106.61	$106.60	$106.60
7 purchase totals =	$514.94		$570.7487	$570.75	$570.65	$570.70