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	$91.69	13.515%	$104.0819	$104.08	$104.10	$104.10
Purchase #2	$112.47	11.283%	$125.16	$125.16	$125.15	$125.20
Purchase #3	$176.94	10.838%	$196.1168	$196.12	$196.10	$196.10
Purchase #4	$82.35	4.629%	$86.162	$86.16	$86.15	$86.20
Purchase #5	$113.76	4.694%	$119.0999	$119.10	$119.10	$119.10
Purchase #6	$76.30	9.546%	$83.5836	$83.58	$83.60	$83.60
Purchase #7	$113.52	12.701%	$127.9382	$127.94	$127.95	$127.90
7 purchase totals =	$767.03		$842.1424	$842.14	$842.15	$842.20