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	$150.48	11.495%	$167.7777	$167.78	$167.80	$167.80
Purchase #2	$73.96	13.192%	$83.7168	$83.72	$83.70	$83.70
Purchase #3	$184.25	7.170%	$197.4607	$197.46	$197.45	$197.50
Purchase #4	$74.90	9.650%	$82.1279	$82.13	$82.15	$82.10
Purchase #5	$74.45	5.315%	$78.407	$78.41	$78.40	$78.40
Purchase #6	$248.32	13.470%	$281.7687	$281.77	$281.75	$281.80
Purchase #7	$10.60	12.419%	$11.9164	$11.92	$11.90	$11.90
7 purchase totals =	$816.96		$903.1752	$903.19	$903.15	$903.20