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	$78.97	13.248%	$89.4319	$89.43	$89.45	$89.40
Purchase #2	$223.34	13.644%	$253.8125	$253.81	$253.80	$253.80
Purchase #3	$116.91	5.486%	$123.3237	$123.32	$123.30	$123.30
Purchase #4	$193.95	5.426%	$204.4737	$204.47	$204.45	$204.50
Purchase #5	$166.99	9.751%	$183.2732	$183.27	$183.25	$183.30
Purchase #6	$54.64	3.484%	$56.5437	$56.54	$56.55	$56.50
Purchase #7	$26.83	11.644%	$29.9541	$29.95	$29.95	$30.00
7 purchase totals =	$861.63		$940.8128	$940.79	$940.75	$940.80