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	$111.78	8.400%	$121.1695	$121.17	$121.15	$121.20
Purchase #2	$125.25	13.301%	$141.9095	$141.91	$141.90	$141.90
Purchase #3	$239.51	13.822%	$272.6151	$272.62	$272.60	$272.60
Purchase #4	$104.33	13.133%	$118.0317	$118.03	$118.05	$118.00
Purchase #5	$154.30	8.377%	$167.2257	$167.23	$167.25	$167.20
Purchase #6	$90.92	10.835%	$100.7712	$100.77	$100.75	$100.80
Purchase #7	$6.25	3.812%	$6.4883	$6.49	$6.50	$6.50
7 purchase totals =	$832.34		$928.2110	$928.22	$928.20	$928.20