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	$104.87	6.637%	$111.8302	$111.83	$111.85	$111.80
Purchase #2	$217.51	11.592%	$242.7238	$242.72	$242.70	$242.70
Purchase #3	$42.69	3.588%	$44.2217	$44.22	$44.20	$44.20
Purchase #4	$217.85	13.429%	$247.1051	$247.11	$247.10	$247.10
Purchase #5	$229.71	11.178%	$255.387	$255.39	$255.40	$255.40
Purchase #6	$48.76	3.163%	$50.3023	$50.30	$50.30	$50.30
Purchase #7	$37.48	4.642%	$39.2198	$39.22	$39.20	$39.20
7 purchase totals =	$898.87		$990.7899	$990.79	$990.75	$990.70