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	$66.96	6.506%	$71.3164	$71.32	$71.30	$71.30
Purchase #2	$46.67	3.838%	$48.4612	$48.46	$48.45	$48.50
Purchase #3	$205.65	8.606%	$223.3482	$223.35	$223.35	$223.30
Purchase #4	$10.86	5.514%	$11.4588	$11.46	$11.45	$11.50
Purchase #5	$167.92	9.726%	$184.2519	$184.25	$184.25	$184.30
Purchase #6	$186.55	5.577%	$196.9539	$196.95	$196.95	$197.00
Purchase #7	$107.80	8.251%	$116.6946	$116.69	$116.70	$116.70
7 purchase totals =	$792.41		$852.4850	$852.48	$852.45	$852.60