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	$22.48	9.826%	$24.6889	$24.69	$24.70	$24.70
Purchase #2	$179.42	9.601%	$196.6461	$196.65	$196.65	$196.60
Purchase #3	$148.74	4.781%	$155.8513	$155.85	$155.85	$155.90
Purchase #4	$62.88	5.779%	$66.5138	$66.51	$66.50	$66.50
Purchase #5	$30.88	10.873%	$34.2376	$34.24	$34.25	$34.20
Purchase #6	$91.69	6.204%	$97.3784	$97.38	$97.40	$97.40
Purchase #7	$16.31	10.450%	$18.0144	$18.01	$18.00	$18.00
7 purchase totals =	$552.40		$593.3305	$593.33	$593.35	$593.30