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	$227.27	3.584%	$235.4154	$235.42	$235.40	$235.40
Purchase #2	$107.33	10.340%	$118.4279	$118.43	$118.45	$118.40
Purchase #3	$114.92	9.855%	$126.2454	$126.25	$126.25	$126.20
Purchase #4	$116.75	10.227%	$128.69	$128.69	$128.70	$128.70
Purchase #5	$90.51	9.630%	$99.2261	$99.23	$99.25	$99.20
Purchase #6	$32.42	4.613%	$33.9155	$33.92	$33.90	$33.90
Purchase #7	$46.85	10.552%	$51.7936	$51.79	$51.80	$51.80
7 purchase totals =	$736.05		$793.7139	$793.73	$793.75	$793.60