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	$246.50	12.664%	$277.7168	$277.72	$277.70	$277.70
Purchase #2	$14.65	5.355%	$15.4345	$15.43	$15.45	$15.40
Purchase #3	$145.72	8.685%	$158.3758	$158.38	$158.40	$158.40
Purchase #4	$116.39	11.654%	$129.9541	$129.95	$129.95	$130.00
Purchase #5	$5.65	3.646%	$5.856	$5.86	$5.85	$5.90
Purchase #6	$55.98	6.686%	$59.7228	$59.72	$59.70	$59.70
Purchase #7	$82.95	7.406%	$89.0933	$89.09	$89.10	$89.10
7 purchase totals =	$667.84		$736.1533	$736.15	$736.15	$736.20