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	$181.57	8.106%	$196.2881	$196.29	$196.30	$196.30
Purchase #2	$71.38	10.382%	$78.7907	$78.79	$78.80	$78.80
Purchase #3	$157.34	13.742%	$178.9617	$178.96	$178.95	$179.00
Purchase #4	$157.79	9.197%	$172.3019	$172.30	$172.30	$172.30
Purchase #5	$70.38	6.806%	$75.1701	$75.17	$75.15	$75.20
Purchase #6	$236.54	3.233%	$244.1873	$244.19	$244.20	$244.20
Purchase #7	$217.60	7.753%	$234.4705	$234.47	$234.45	$234.50
7 purchase totals =	$1,092.60		$1,180.1703	$1,180.17	$1,180.15	$1,180.30