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	$156.44	5.366%	$164.8346	$164.83	$164.85	$164.80
Purchase #2	$245.61	12.304%	$275.8299	$275.83	$275.85	$275.80
Purchase #3	$159.90	5.191%	$168.2004	$168.20	$168.20	$168.20
Purchase #4	$173.47	13.209%	$196.3837	$196.38	$196.40	$196.40
Purchase #5	$77.90	12.491%	$87.6305	$87.63	$87.65	$87.60
Purchase #6	$52.96	4.447%	$55.3151	$55.32	$55.30	$55.30
Purchase #7	$248.79	5.724%	$263.0307	$263.03	$263.05	$263.00
7 purchase totals =	$1,115.07		$1,211.2249	$1,211.22	$1,211.30	$1,211.10