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	$234.38	5.433%	$247.1139	$247.11	$247.10	$247.10
Purchase #2	$76.86	11.524%	$85.7173	$85.72	$85.70	$85.70
Purchase #3	$231.49	12.321%	$260.0119	$260.01	$260.00	$260.00
Purchase #4	$229.68	10.842%	$254.5819	$254.58	$254.60	$254.60
Purchase #5	$76.76	7.761%	$82.7173	$82.72	$82.70	$82.70
Purchase #6	$168.95	9.536%	$185.0611	$185.06	$185.05	$185.10
Purchase #7	$32.72	3.243%	$33.7811	$33.78	$33.80	$33.80
7 purchase totals =	$1,050.84		$1,148.9845	$1,148.98	$1,148.95	$1,149.00