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	$34.38	5.108%	$36.1361	$36.14	$36.15	$36.10
Purchase #2	$206.62	13.214%	$233.9228	$233.92	$233.90	$233.90
Purchase #3	$241.32	6.410%	$256.7886	$256.79	$256.80	$256.80
Purchase #4	$36.56	6.305%	$38.8651	$38.87	$38.85	$38.90
Purchase #5	$155.71	11.338%	$173.3644	$173.36	$173.35	$173.40
Purchase #6	$246.57	9.190%	$269.2298	$269.23	$269.25	$269.20
Purchase #7	$100.51	10.712%	$111.2766	$111.28	$111.30	$111.30
7 purchase totals =	$1,021.67		$1,119.5834	$1,119.59	$1,119.60	$1,119.60