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	$114.99	13.401%	$130.3998	$130.40	$130.40	$130.40
Purchase #2	$248.38	10.411%	$274.2388	$274.24	$274.25	$274.20
Purchase #3	$19.54	7.861%	$21.076	$21.08	$21.10	$21.10
Purchase #4	$6.83	4.373%	$7.1287	$7.13	$7.15	$7.10
Purchase #5	$156.60	5.426%	$165.0971	$165.10	$165.10	$165.10
Purchase #6	$64.32	11.367%	$71.6313	$71.63	$71.65	$71.60
Purchase #7	$10.90	7.441%	$11.7111	$11.71	$11.70	$11.70
7 purchase totals =	$621.56		$681.2828	$681.29	$681.35	$681.20