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	$30.57	13.287%	$34.6318	$34.63	$34.65	$34.60
Purchase #2	$54.74	11.743%	$61.1681	$61.17	$61.15	$61.20
Purchase #3	$171.31	5.722%	$181.1124	$181.11	$181.10	$181.10
Purchase #4	$131.86	12.570%	$148.4348	$148.43	$148.45	$148.40
Purchase #5	$116.79	12.580%	$131.4822	$131.48	$131.50	$131.50
Purchase #6	$23.68	5.740%	$25.0392	$25.04	$25.05	$25.00
Purchase #7	$65.34	9.450%	$71.5146	$71.51	$71.50	$71.50
7 purchase totals =	$594.29		$653.3831	$653.37	$653.40	$653.30