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	$15.70	10.376%	$17.329	$17.33	$17.35	$17.30
Purchase #2	$184.44	13.776%	$209.8485	$209.85	$209.85	$209.80
Purchase #3	$147.87	6.157%	$156.9744	$156.97	$156.95	$157.00
Purchase #4	$220.42	13.279%	$249.6896	$249.69	$249.70	$249.70
Purchase #5	$74.34	5.794%	$78.6473	$78.65	$78.65	$78.60
Purchase #6	$231.40	12.386%	$260.0612	$260.06	$260.05	$260.10
Purchase #7	$211.79	5.729%	$223.9234	$223.92	$223.90	$223.90
7 purchase totals =	$1,085.96		$1,196.4734	$1,196.47	$1,196.45	$1,196.40