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	$105.36	5.775%	$111.4445	$111.44	$111.45	$111.40
Purchase #2	$83.62	7.399%	$89.807	$89.81	$89.80	$89.80
Purchase #3	$207.70	6.643%	$221.4975	$221.50	$221.50	$221.50
Purchase #4	$164.36	6.663%	$175.3113	$175.31	$175.30	$175.30
Purchase #5	$21.72	10.509%	$24.0026	$24.00	$24.00	$24.00
Purchase #6	$166.54	8.537%	$180.7575	$180.76	$180.75	$180.80
Purchase #7	$9.61	9.103%	$10.4848	$10.48	$10.50	$10.50
7 purchase totals =	$758.91		$813.3052	$813.30	$813.30	$813.30