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	$226.51	13.406%	$256.8759	$256.88	$256.90	$256.90
Purchase #2	$171.37	10.449%	$189.2765	$189.28	$189.30	$189.30
Purchase #3	$173.53	9.118%	$189.3525	$189.35	$189.35	$189.40
Purchase #4	$61.42	6.536%	$65.4344	$65.43	$65.45	$65.40
Purchase #5	$244.27	13.201%	$276.5161	$276.52	$276.50	$276.50
Purchase #6	$87.61	5.250%	$92.2095	$92.21	$92.20	$92.20
Purchase #7	$165.67	13.142%	$187.4424	$187.44	$187.45	$187.40
7 purchase totals =	$1,130.38		$1,257.1073	$1,257.11	$1,257.15	$1,257.10