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	$155.77	5.371%	$164.1364	$164.14	$164.15	$164.10
Purchase #2	$102.29	3.506%	$105.8763	$105.88	$105.90	$105.90
Purchase #3	$224.54	13.757%	$255.43	$255.43	$255.45	$255.40
Purchase #4	$133.72	12.325%	$150.201	$150.20	$150.20	$150.20
Purchase #5	$108.40	10.626%	$119.9186	$119.92	$119.90	$119.90
Purchase #6	$61.98	10.300%	$68.3639	$68.36	$68.35	$68.40
Purchase #7	$66.95	10.737%	$74.1384	$74.14	$74.15	$74.10
7 purchase totals =	$853.65		$938.0646	$938.07	$938.10	$938.00