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	$241.25	5.460%	$254.4223	$254.42	$254.40	$254.40
Purchase #2	$116.72	13.248%	$132.1831	$132.18	$132.20	$132.20
Purchase #3	$122.87	3.687%	$127.4002	$127.40	$127.40	$127.40
Purchase #4	$92.39	11.492%	$103.0075	$103.01	$103.00	$103.00
Purchase #5	$102.91	13.260%	$116.5559	$116.56	$116.55	$116.60
Purchase #6	$139.96	6.211%	$148.6529	$148.65	$148.65	$148.70
Purchase #7	$32.80	11.524%	$36.5799	$36.58	$36.60	$36.60
7 purchase totals =	$848.90		$918.8018	$918.80	$918.80	$918.90