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	$147.60	5.572%	$155.8243	$155.82	$155.80	$155.80
Purchase #2	$172.33	4.396%	$179.9056	$179.91	$179.90	$179.90
Purchase #3	$17.73	12.592%	$19.9626	$19.96	$19.95	$20.00
Purchase #4	$105.40	8.241%	$114.086	$114.09	$114.10	$114.10
Purchase #5	$126.35	8.542%	$137.1428	$137.14	$137.15	$137.10
Purchase #6	$182.42	5.431%	$192.3272	$192.33	$192.35	$192.30
Purchase #7	$89.92	12.122%	$100.8201	$100.82	$100.80	$100.80
7 purchase totals =	$841.75		$900.0686	$900.07	$900.05	$900.00