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	$41.46	12.323%	$46.5691	$46.57	$46.55	$46.60
Purchase #2	$199.80	8.705%	$217.1926	$217.19	$217.20	$217.20
Purchase #3	$38.51	13.378%	$43.6619	$43.66	$43.65	$43.70
Purchase #4	$190.46	3.213%	$196.5795	$196.58	$196.60	$196.60
Purchase #5	$141.64	8.414%	$153.5576	$153.56	$153.55	$153.60
Purchase #6	$77.41	3.867%	$80.4034	$80.40	$80.40	$80.40
Purchase #7	$79.80	11.728%	$89.1589	$89.16	$89.15	$89.20
7 purchase totals =	$769.08		$827.1230	$827.12	$827.10	$827.30