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	$159.99	12.106%	$179.3584	$179.36	$179.35	$179.40
Purchase #2	$151.99	8.660%	$165.1523	$165.15	$165.15	$165.20
Purchase #3	$93.73	12.650%	$105.5868	$105.59	$105.60	$105.60
Purchase #4	$45.89	13.613%	$52.137	$52.14	$52.15	$52.10
Purchase #5	$130.92	3.189%	$135.095	$135.10	$135.10	$135.10
Purchase #6	$38.33	6.686%	$40.8927	$40.89	$40.90	$40.90
Purchase #7	$145.86	7.644%	$157.0095	$157.01	$157.00	$157.00
7 purchase totals =	$766.71		$835.2317	$835.24	$835.25	$835.30