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	$11.65	10.531%	$12.8769	$12.88	$12.90	$12.90
Purchase #2	$157.34	5.825%	$166.5051	$166.51	$166.50	$166.50
Purchase #3	$128.95	10.396%	$142.3556	$142.36	$142.35	$142.40
Purchase #4	$69.92	11.675%	$78.0832	$78.08	$78.10	$78.10
Purchase #5	$125.94	5.191%	$132.4775	$132.48	$132.50	$132.50
Purchase #6	$147.43	5.813%	$156.0001	$156.00	$156.00	$156.00
Purchase #7	$198.52	12.469%	$223.2735	$223.27	$223.25	$223.30
7 purchase totals =	$839.75		$911.5719	$911.58	$911.60	$911.70