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	$92.72	13.121%	$104.8858	$104.89	$104.90	$104.90
Purchase #2	$46.95	8.754%	$51.06	$51.06	$51.05	$51.10
Purchase #3	$43.58	10.301%	$48.0692	$48.07	$48.05	$48.10
Purchase #4	$89.89	11.726%	$100.4305	$100.43	$100.45	$100.40
Purchase #5	$76.83	8.546%	$83.3959	$83.40	$83.40	$83.40
Purchase #6	$46.68	10.106%	$51.3975	$51.40	$51.40	$51.40
Purchase #7	$202.49	9.400%	$221.5241	$221.52	$221.50	$221.50
7 purchase totals =	$599.14		$660.7630	$660.77	$660.75	$660.80