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	$54.88	6.508%	$58.4516	$58.45	$58.45	$58.50
Purchase #2	$72.52	11.745%	$81.0375	$81.04	$81.05	$81.00
Purchase #3	$85.90	10.137%	$94.6077	$94.61	$94.60	$94.60
Purchase #4	$195.82	8.566%	$212.5939	$212.59	$212.60	$212.60
Purchase #5	$19.49	9.234%	$21.2897	$21.29	$21.30	$21.30
Purchase #6	$144.53	4.119%	$150.4832	$150.48	$150.50	$150.50
Purchase #7	$19.64	4.198%	$20.4645	$20.46	$20.45	$20.50
7 purchase totals =	$592.78		$638.9281	$638.92	$638.95	$639.00