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	$92.52	11.667%	$103.3143	$103.31	$103.30	$103.30
Purchase #2	$79.93	3.584%	$82.7947	$82.79	$82.80	$82.80
Purchase #3	$46.92	12.491%	$52.7808	$52.78	$52.80	$52.80
Purchase #4	$152.25	13.514%	$172.8251	$172.83	$172.85	$172.80
Purchase #5	$30.90	4.721%	$32.3588	$32.36	$32.35	$32.40
Purchase #6	$34.68	13.753%	$39.4495	$39.45	$39.45	$39.40
Purchase #7	$181.55	10.550%	$200.7035	$200.70	$200.70	$200.70
7 purchase totals =	$618.75		$684.2267	$684.22	$684.25	$684.20