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	$120.37	6.325%	$127.9834	$127.98	$128.00	$128.00
Purchase #2	$241.52	5.666%	$255.2045	$255.20	$255.20	$255.20
Purchase #3	$68.96	11.396%	$76.8187	$76.82	$76.80	$76.80
Purchase #4	$228.82	9.830%	$251.313	$251.31	$251.30	$251.30
Purchase #5	$104.51	13.165%	$118.2687	$118.27	$118.25	$118.30
Purchase #6	$97.42	3.395%	$100.7274	$100.73	$100.75	$100.70
Purchase #7	$33.82	6.626%	$36.0609	$36.06	$36.05	$36.10
7 purchase totals =	$895.42		$966.3766	$966.37	$966.35	$966.40