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	$73.54	8.579%	$79.849	$79.85	$79.85	$79.80
Purchase #2	$121.74	5.169%	$128.0327	$128.03	$128.05	$128.00
Purchase #3	$208.95	3.838%	$216.9695	$216.97	$216.95	$217.00
Purchase #4	$38.43	10.523%	$42.474	$42.47	$42.45	$42.50
Purchase #5	$160.52	7.231%	$172.1272	$172.13	$172.15	$172.10
Purchase #6	$128.57	6.538%	$136.9759	$136.98	$137.00	$137.00
Purchase #7	$246.41	13.275%	$279.1209	$279.12	$279.10	$279.10
7 purchase totals =	$978.16		$1,055.5492	$1,055.55	$1,055.55	$1,055.50