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	$162.56	13.691%	$184.8161	$184.82	$184.80	$184.80
Purchase #2	$145.30	10.726%	$160.8849	$160.88	$160.90	$160.90
Purchase #3	$70.39	4.258%	$73.3872	$73.39	$73.40	$73.40
Purchase #4	$230.99	9.166%	$252.1625	$252.16	$252.15	$252.20
Purchase #5	$219.54	5.352%	$231.2898	$231.29	$231.30	$231.30
Purchase #6	$54.54	9.616%	$59.7846	$59.78	$59.80	$59.80
Purchase #7	$37.53	6.439%	$39.9466	$39.95	$39.95	$39.90
7 purchase totals =	$920.85		$1,002.2717	$1,002.27	$1,002.30	$1,002.30