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	$245.76	13.266%	$278.3625	$278.36	$278.35	$278.40
Purchase #2	$12.43	5.321%	$13.0914	$13.09	$13.10	$13.10
Purchase #3	$74.59	3.226%	$76.9963	$77.00	$77.00	$77.00
Purchase #4	$57.74	7.426%	$62.0278	$62.03	$62.05	$62.00
Purchase #5	$30.58	6.265%	$32.4958	$32.50	$32.50	$32.50
Purchase #6	$60.87	12.414%	$68.4264	$68.43	$68.45	$68.40
Purchase #7	$78.77	13.653%	$89.5245	$89.52	$89.50	$89.50
7 purchase totals =	$560.74		$620.9247	$620.93	$620.95	$620.90