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	$203.68	9.117%	$222.2495	$222.25	$222.25	$222.20
Purchase #2	$241.34	6.718%	$257.5532	$257.55	$257.55	$257.60
Purchase #3	$95.73	4.404%	$99.9459	$99.95	$99.95	$99.90
Purchase #4	$118.53	4.530%	$123.8994	$123.90	$123.90	$123.90
Purchase #5	$148.41	3.852%	$154.1268	$154.13	$154.15	$154.10
Purchase #6	$65.34	8.442%	$70.856	$70.86	$70.85	$70.90
Purchase #7	$55.44	9.190%	$60.5349	$60.53	$60.55	$60.50
7 purchase totals =	$928.47		$989.1657	$989.17	$989.20	$989.10