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	$179.63	10.835%	$199.0929	$199.09	$199.10	$199.10
Purchase #2	$159.69	13.591%	$181.3935	$181.39	$181.40	$181.40
Purchase #3	$235.51	5.446%	$248.3359	$248.34	$248.35	$248.30
Purchase #4	$101.73	9.360%	$111.2519	$111.25	$111.25	$111.30
Purchase #5	$198.56	3.715%	$205.9365	$205.94	$205.95	$205.90
Purchase #6	$160.96	12.743%	$181.4711	$181.47	$181.45	$181.50
Purchase #7	$233.40	13.255%	$264.3372	$264.34	$264.35	$264.30
7 purchase totals =	$1,269.48		$1,391.8190	$1,391.82	$1,391.85	$1,391.80