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	$70.85	11.413%	$78.9361	$78.94	$78.95	$78.90
Purchase #2	$46.43	10.727%	$51.4105	$51.41	$51.40	$51.40
Purchase #3	$190.45	13.513%	$216.1855	$216.19	$216.20	$216.20
Purchase #4	$141.86	7.808%	$152.9364	$152.94	$152.95	$152.90
Purchase #5	$244.42	5.698%	$258.3471	$258.35	$258.35	$258.30
Purchase #6	$214.75	7.642%	$231.1612	$231.16	$231.15	$231.20
Purchase #7	$139.70	9.371%	$152.7913	$152.79	$152.80	$152.80
7 purchase totals =	$1,048.46		$1,141.7681	$1,141.78	$1,141.80	$1,141.70