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	$133.44	12.504%	$150.1253	$150.13	$150.15	$150.10
Purchase #2	$233.70	10.491%	$258.2175	$258.22	$258.20	$258.20
Purchase #3	$52.29	7.510%	$56.217	$56.22	$56.20	$56.20
Purchase #4	$43.33	5.807%	$45.8462	$45.85	$45.85	$45.80
Purchase #5	$90.67	8.271%	$98.1693	$98.17	$98.15	$98.20
Purchase #6	$164.44	4.616%	$172.0306	$172.03	$172.05	$172.00
Purchase #7	$90.32	10.855%	$100.1242	$100.12	$100.10	$100.10
7 purchase totals =	$808.19		$880.7301	$880.74	$880.70	$880.60