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	$37.39	7.680%	$40.2616	$40.26	$40.25	$40.30
Purchase #2	$93.44	11.602%	$104.2809	$104.28	$104.30	$104.30
Purchase #3	$148.34	3.320%	$153.2649	$153.26	$153.25	$153.30
Purchase #4	$103.79	7.114%	$111.1736	$111.17	$111.15	$111.20
Purchase #5	$134.42	7.373%	$144.3308	$144.33	$144.35	$144.30
Purchase #6	$79.77	6.151%	$84.6767	$84.68	$84.70	$84.70
Purchase #7	$57.57	8.445%	$62.4318	$62.43	$62.45	$62.40
7 purchase totals =	$654.72		$700.4203	$700.41	$700.45	$700.50