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	$127.43	12.109%	$142.8605	$142.86	$142.85	$142.90
Purchase #2	$134.50	10.203%	$148.223	$148.22	$148.20	$148.20
Purchase #3	$183.87	13.529%	$208.7458	$208.75	$208.75	$208.70
Purchase #4	$70.96	8.711%	$77.1413	$77.14	$77.15	$77.10
Purchase #5	$40.85	11.587%	$45.5833	$45.58	$45.60	$45.60
Purchase #6	$51.34	6.281%	$54.5647	$54.56	$54.55	$54.60
Purchase #7	$86.63	10.110%	$95.3883	$95.39	$95.40	$95.40
7 purchase totals =	$695.58		$772.5069	$772.50	$772.50	$772.50