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	$12.86	5.731%	$13.597	$13.60	$13.60	$13.60
Purchase #2	$113.35	13.806%	$128.9991	$129.00	$129.00	$129.00
Purchase #3	$50.99	4.544%	$53.307	$53.31	$53.30	$53.30
Purchase #4	$150.44	8.254%	$162.8573	$162.86	$162.85	$162.90
Purchase #5	$33.90	9.806%	$37.2242	$37.22	$37.20	$37.20
Purchase #6	$101.30	9.836%	$111.2639	$111.26	$111.25	$111.30
Purchase #7	$231.64	6.820%	$247.4378	$247.44	$247.45	$247.40
7 purchase totals =	$694.48		$754.6863	$754.69	$754.65	$754.70