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	$52.79	13.460%	$59.8955	$59.90	$59.90	$59.90
Purchase #2	$85.59	5.205%	$90.045	$90.05	$90.05	$90.00
Purchase #3	$14.73	6.194%	$15.6424	$15.64	$15.65	$15.60
Purchase #4	$158.65	8.337%	$171.8767	$171.88	$171.90	$171.90
Purchase #5	$179.31	10.719%	$198.5302	$198.53	$198.55	$198.50
Purchase #6	$24.73	8.491%	$26.8298	$26.83	$26.85	$26.80
Purchase #7	$107.60	7.343%	$115.5011	$115.50	$115.50	$115.50
7 purchase totals =	$623.40		$678.3207	$678.33	$678.40	$678.20