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	$9.49	3.367%	$9.8095	$9.81	$9.80	$9.80
Purchase #2	$189.81	3.702%	$196.8368	$196.84	$196.85	$196.80
Purchase #3	$159.87	4.287%	$166.7236	$166.72	$166.70	$166.70
Purchase #4	$70.92	10.643%	$78.468	$78.47	$78.45	$78.50
Purchase #5	$95.74	10.246%	$105.5495	$105.55	$105.55	$105.50
Purchase #6	$93.97	4.136%	$97.8566	$97.86	$97.85	$97.90
Purchase #7	$178.77	11.410%	$199.1677	$199.17	$199.15	$199.20
7 purchase totals =	$798.57		$854.4117	$854.42	$854.35	$854.40