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	$205.46	5.338%	$216.4275	$216.43	$216.45	$216.40
Purchase #2	$174.98	8.306%	$189.5138	$189.51	$189.50	$189.50
Purchase #3	$233.56	8.520%	$253.4593	$253.46	$253.45	$253.50
Purchase #4	$46.31	3.672%	$48.0105	$48.01	$48.00	$48.00
Purchase #5	$125.60	13.682%	$142.7846	$142.78	$142.80	$142.80
Purchase #6	$18.82	10.669%	$20.8279	$20.83	$20.85	$20.80
Purchase #7	$18.97	7.411%	$20.3759	$20.38	$20.40	$20.40
7 purchase totals =	$823.70		$891.3995	$891.40	$891.45	$891.40