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	$50.51	7.271%	$54.1826	$54.18	$54.20	$54.20
Purchase #2	$148.41	8.590%	$161.1584	$161.16	$161.15	$161.20
Purchase #3	$167.34	5.396%	$176.3697	$176.37	$176.35	$176.40
Purchase #4	$131.30	7.269%	$140.8442	$140.84	$140.85	$140.80
Purchase #5	$68.59	4.151%	$71.4372	$71.44	$71.45	$71.40
Purchase #6	$56.47	11.153%	$62.7681	$62.77	$62.75	$62.80
Purchase #7	$143.54	6.679%	$153.127	$153.13	$153.15	$153.10
7 purchase totals =	$766.16		$819.8872	$819.89	$819.90	$819.90