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	$142.38	6.280%	$151.3215	$151.32	$151.30	$151.30
Purchase #2	$71.88	7.201%	$77.0561	$77.06	$77.05	$77.10
Purchase #3	$175.56	9.607%	$192.426	$192.43	$192.45	$192.40
Purchase #4	$49.47	6.505%	$52.688	$52.69	$52.70	$52.70
Purchase #5	$129.27	3.269%	$133.4958	$133.50	$133.50	$133.50
Purchase #6	$29.98	11.566%	$33.4475	$33.45	$33.45	$33.40
Purchase #7	$144.36	4.167%	$150.3755	$150.38	$150.40	$150.40
7 purchase totals =	$742.90		$790.8104	$790.83	$790.85	$790.80