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	$233.31	9.288%	$254.9798	$254.98	$255.00	$255.00
Purchase #2	$29.46	11.707%	$32.9089	$32.91	$32.90	$32.90
Purchase #3	$163.82	10.294%	$180.6836	$180.68	$180.70	$180.70
Purchase #4	$26.44	3.178%	$27.2803	$27.28	$27.30	$27.30
Purchase #5	$162.61	3.390%	$168.1225	$168.12	$168.10	$168.10
Purchase #6	$148.78	3.321%	$153.721	$153.72	$153.70	$153.70
Purchase #7	$139.35	11.829%	$155.8337	$155.83	$155.85	$155.80
7 purchase totals =	$903.77		$973.5298	$973.52	$973.55	$973.50