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	$114.82	13.320%	$130.114	$130.11	$130.10	$130.10
Purchase #2	$42.31	8.366%	$45.8497	$45.85	$45.85	$45.80
Purchase #3	$55.36	3.485%	$57.2893	$57.29	$57.30	$57.30
Purchase #4	$54.40	4.726%	$56.9709	$56.97	$56.95	$57.00
Purchase #5	$138.37	7.228%	$148.3714	$148.37	$148.35	$148.40
Purchase #6	$232.46	6.762%	$248.1789	$248.18	$248.20	$248.20
Purchase #7	$89.58	11.162%	$99.5789	$99.58	$99.60	$99.60
7 purchase totals =	$727.30		$786.3531	$786.35	$786.35	$786.40