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	$10.51	10.224%	$11.5845	$11.58	$11.60	$11.60
Purchase #2	$140.37	11.123%	$155.9834	$155.98	$156.00	$156.00
Purchase #3	$19.31	5.718%	$20.4141	$20.41	$20.40	$20.40
Purchase #4	$202.47	8.860%	$220.4088	$220.41	$220.40	$220.40
Purchase #5	$233.85	7.312%	$250.9491	$250.95	$250.95	$250.90
Purchase #6	$197.53	9.578%	$216.4494	$216.45	$216.45	$216.40
Purchase #7	$128.89	6.704%	$137.5308	$137.53	$137.55	$137.50
7 purchase totals =	$932.93		$1,013.3201	$1,013.31	$1,013.35	$1,013.20