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	$11.82	9.779%	$12.9759	$12.98	$13.00	$13.00
Purchase #2	$171.47	10.606%	$189.6561	$189.66	$189.65	$189.70
Purchase #3	$160.95	7.347%	$172.775	$172.78	$172.80	$172.80
Purchase #4	$155.95	5.766%	$164.9421	$164.94	$164.95	$164.90
Purchase #5	$234.42	3.836%	$243.4124	$243.41	$243.40	$243.40
Purchase #6	$157.92	13.388%	$179.0623	$179.06	$179.05	$179.10
Purchase #7	$95.39	7.848%	$102.8762	$102.88	$102.90	$102.90
7 purchase totals =	$987.92		$1,065.7000	$1,065.71	$1,065.75	$1,065.80