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	$161.44	5.622%	$170.5162	$170.52	$170.50	$170.50
Purchase #2	$234.62	3.806%	$243.5496	$243.55	$243.55	$243.50
Purchase #3	$128.94	11.300%	$143.5102	$143.51	$143.50	$143.50
Purchase #4	$129.47	3.295%	$133.736	$133.74	$133.75	$133.70
Purchase #5	$87.53	3.395%	$90.5016	$90.50	$90.50	$90.50
Purchase #6	$148.59	6.255%	$157.8843	$157.88	$157.90	$157.90
Purchase #7	$132.83	13.691%	$151.0158	$151.02	$151.00	$151.00
7 purchase totals =	$1,023.42		$1,090.7137	$1,090.72	$1,090.70	$1,090.60