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	$66.80	11.313%	$74.3571	$74.36	$74.35	$74.40
Purchase #2	$178.59	11.575%	$199.2618	$199.26	$199.25	$199.30
Purchase #3	$147.29	12.171%	$165.2167	$165.22	$165.20	$165.20
Purchase #4	$169.80	8.683%	$184.5437	$184.54	$184.55	$184.50
Purchase #5	$41.56	9.390%	$45.4625	$45.46	$45.45	$45.50
Purchase #6	$84.29	3.151%	$86.946	$86.95	$86.95	$86.90
Purchase #7	$178.91	3.449%	$185.0806	$185.08	$185.10	$185.10
7 purchase totals =	$867.24		$940.8684	$940.87	$940.85	$940.90