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	$37.65	6.104%	$39.9482	$39.95	$39.95	$39.90
Purchase #2	$47.50	8.429%	$51.5038	$51.50	$51.50	$51.50
Purchase #3	$116.37	5.829%	$123.1532	$123.15	$123.15	$123.20
Purchase #4	$229.67	12.816%	$259.1045	$259.10	$259.10	$259.10
Purchase #5	$184.97	10.706%	$204.7729	$204.77	$204.75	$204.80
Purchase #6	$173.57	12.634%	$195.4988	$195.50	$195.50	$195.50
Purchase #7	$87.87	13.600%	$99.8203	$99.82	$99.80	$99.80
7 purchase totals =	$877.60		$973.8017	$973.79	$973.75	$973.80