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	$48.63	4.332%	$50.7367	$50.74	$50.75	$50.70
Purchase #2	$194.64	10.373%	$214.83	$214.83	$214.85	$214.80
Purchase #3	$238.90	6.258%	$253.8504	$253.85	$253.85	$253.90
Purchase #4	$37.59	8.629%	$40.8336	$40.83	$40.85	$40.80
Purchase #5	$114.71	7.700%	$123.5427	$123.54	$123.55	$123.50
Purchase #6	$235.59	13.631%	$267.7033	$267.70	$267.70	$267.70
Purchase #7	$19.74	6.370%	$20.9974	$21.00	$21.00	$21.00
7 purchase totals =	$889.80		$972.4941	$972.49	$972.55	$972.40