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	$79.32	12.315%	$89.0883	$89.09	$89.10	$89.10
Purchase #2	$107.49	10.444%	$118.7163	$118.72	$118.70	$118.70
Purchase #3	$93.27	11.466%	$103.9643	$103.96	$103.95	$104.00
Purchase #4	$96.44	6.837%	$103.0336	$103.03	$103.05	$103.00
Purchase #5	$204.51	4.465%	$213.6414	$213.64	$213.65	$213.60
Purchase #6	$117.57	8.708%	$127.808	$127.81	$127.80	$127.80
Purchase #7	$188.96	5.548%	$199.4435	$199.44	$199.45	$199.40
7 purchase totals =	$887.56		$955.6954	$955.69	$955.70	$955.60