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	$247.77	12.757%	$279.378	$279.38	$279.40	$279.40
Purchase #2	$30.60	4.771%	$32.0599	$32.06	$32.05	$32.10
Purchase #3	$51.67	7.574%	$55.5835	$55.58	$55.60	$55.60
Purchase #4	$143.76	6.504%	$153.1102	$153.11	$153.10	$153.10
Purchase #5	$151.69	3.188%	$156.5259	$156.53	$156.55	$156.50
Purchase #6	$243.54	3.319%	$251.6231	$251.62	$251.60	$251.60
Purchase #7	$215.53	5.254%	$226.8539	$226.85	$226.85	$226.90
7 purchase totals =	$1,084.56		$1,155.1345	$1,155.13	$1,155.15	$1,155.20