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	$238.78	13.102%	$270.065	$270.07	$270.05	$270.10
Purchase #2	$197.45	11.150%	$219.4657	$219.47	$219.45	$219.50
Purchase #3	$49.29	10.322%	$54.3777	$54.38	$54.40	$54.40
Purchase #4	$160.92	6.858%	$171.9559	$171.96	$171.95	$172.00
Purchase #5	$154.42	12.321%	$173.4461	$173.45	$173.45	$173.40
Purchase #6	$240.66	3.654%	$249.4537	$249.45	$249.45	$249.50
Purchase #7	$32.90	3.555%	$34.0696	$34.07	$34.05	$34.10
7 purchase totals =	$1,074.42		$1,172.8337	$1,172.85	$1,172.80	$1,173.00