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	$121.89	12.435%	$137.047	$137.05	$137.05	$137.00
Purchase #2	$40.29	12.330%	$45.2578	$45.26	$45.25	$45.30
Purchase #3	$99.86	12.684%	$112.5262	$112.53	$112.55	$112.50
Purchase #4	$38.55	11.757%	$43.0823	$43.08	$43.10	$43.10
Purchase #5	$138.44	7.136%	$148.3191	$148.32	$148.30	$148.30
Purchase #6	$40.85	10.485%	$45.1331	$45.13	$45.15	$45.10
Purchase #7	$159.62	9.819%	$175.2931	$175.29	$175.30	$175.30
7 purchase totals =	$639.50		$706.6586	$706.66	$706.70	$706.60