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	$51.30	12.335%	$57.6279	$57.63	$57.65	$57.60
Purchase #2	$29.73	8.375%	$32.2199	$32.22	$32.20	$32.20
Purchase #3	$117.91	4.398%	$123.0957	$123.10	$123.10	$123.10
Purchase #4	$121.40	5.756%	$128.3878	$128.39	$128.40	$128.40
Purchase #5	$225.69	13.131%	$255.3254	$255.33	$255.35	$255.30
Purchase #6	$98.59	13.303%	$111.7054	$111.71	$111.70	$111.70
Purchase #7	$45.60	11.805%	$50.9831	$50.98	$51.00	$51.00
7 purchase totals =	$690.22		$759.3452	$759.36	$759.40	$759.30