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	$249.85	6.661%	$266.4925	$266.49	$266.50	$266.50
Purchase #2	$186.78	9.151%	$203.8722	$203.87	$203.85	$203.90
Purchase #3	$97.98	5.854%	$103.7157	$103.72	$103.70	$103.70
Purchase #4	$246.25	3.364%	$254.5339	$254.53	$254.55	$254.50
Purchase #5	$56.68	5.228%	$59.6432	$59.64	$59.65	$59.60
Purchase #6	$189.44	4.298%	$197.5821	$197.58	$197.60	$197.60
Purchase #7	$14.30	4.613%	$14.9597	$14.96	$14.95	$15.00
7 purchase totals =	$1,041.28		$1,100.7993	$1,100.79	$1,100.80	$1,100.80