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	$201.66	7.255%	$216.2904	$216.29	$216.30	$216.30
Purchase #2	$209.95	11.131%	$233.3195	$233.32	$233.30	$233.30
Purchase #3	$249.75	4.777%	$261.6806	$261.68	$261.70	$261.70
Purchase #4	$116.35	9.322%	$127.1961	$127.20	$127.20	$127.20
Purchase #5	$78.78	13.159%	$89.1467	$89.15	$89.15	$89.10
Purchase #6	$72.88	7.355%	$78.2403	$78.24	$78.25	$78.20
Purchase #7	$108.98	3.206%	$112.4739	$112.47	$112.45	$112.50
7 purchase totals =	$1,038.35		$1,118.3475	$1,118.35	$1,118.35	$1,118.30