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	$33.80	10.273%	$37.2723	$37.27	$37.25	$37.30
Purchase #2	$154.49	8.719%	$167.96	$167.96	$167.95	$168.00
Purchase #3	$11.29	11.594%	$12.599	$12.60	$12.60	$12.60
Purchase #4	$219.88	13.157%	$248.8096	$248.81	$248.80	$248.80
Purchase #5	$205.57	4.388%	$214.5904	$214.59	$214.60	$214.60
Purchase #6	$68.72	13.805%	$78.2068	$78.21	$78.20	$78.20
Purchase #7	$76.25	13.321%	$86.4073	$86.41	$86.40	$86.40
7 purchase totals =	$770.00		$845.8454	$845.85	$845.80	$845.90