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	$79.47	7.819%	$85.6838	$85.68	$85.70	$85.70
Purchase #2	$142.89	5.405%	$150.6132	$150.61	$150.60	$150.60
Purchase #3	$115.94	10.328%	$127.9143	$127.91	$127.90	$127.90
Purchase #4	$38.62	7.806%	$41.6347	$41.63	$41.65	$41.60
Purchase #5	$164.80	13.480%	$187.015	$187.02	$187.00	$187.00
Purchase #6	$89.68	11.613%	$100.0945	$100.09	$100.10	$100.10
Purchase #7	$172.50	8.425%	$187.0331	$187.03	$187.05	$187.00
7 purchase totals =	$803.90		$879.9886	$879.97	$880.00	$879.90