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	$75.85	12.297%	$85.1773	$85.18	$85.20	$85.20
Purchase #2	$18.64	13.444%	$21.146	$21.15	$21.15	$21.10
Purchase #3	$86.90	4.482%	$90.7949	$90.79	$90.80	$90.80
Purchase #4	$197.30	12.210%	$221.3903	$221.39	$221.40	$221.40
Purchase #5	$109.82	11.746%	$122.7195	$122.72	$122.70	$122.70
Purchase #6	$204.59	10.762%	$226.608	$226.61	$226.60	$226.60
Purchase #7	$60.40	12.174%	$67.7531	$67.75	$67.75	$67.80
7 purchase totals =	$753.50		$835.5891	$835.59	$835.60	$835.60