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	$101.26	13.863%	$115.2977	$115.30	$115.30	$115.30
Purchase #2	$105.26	6.194%	$111.7798	$111.78	$111.80	$111.80
Purchase #3	$54.88	9.161%	$59.9076	$59.91	$59.90	$59.90
Purchase #4	$42.35	6.418%	$45.068	$45.07	$45.05	$45.10
Purchase #5	$64.73	10.461%	$71.5014	$71.50	$71.50	$71.50
Purchase #6	$52.85	12.327%	$59.3648	$59.36	$59.35	$59.40
Purchase #7	$169.40	10.437%	$187.0803	$187.08	$187.10	$187.10
7 purchase totals =	$590.73		$649.9996	$650.00	$650.00	$650.10