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	$22.51	8.725%	$24.474	$24.47	$24.45	$24.50
Purchase #2	$99.48	5.349%	$104.8012	$104.80	$104.80	$104.80
Purchase #3	$98.71	5.833%	$104.4678	$104.47	$104.45	$104.50
Purchase #4	$21.57	4.436%	$22.5268	$22.53	$22.55	$22.50
Purchase #5	$241.80	9.286%	$264.2535	$264.25	$264.25	$264.30
Purchase #6	$164.71	5.815%	$174.2879	$174.29	$174.30	$174.30
Purchase #7	$75.49	3.747%	$78.3186	$78.32	$78.30	$78.30
7 purchase totals =	$724.27		$773.1298	$773.13	$773.10	$773.20