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	$245.82	12.336%	$276.1444	$276.14	$276.15	$276.10
Purchase #2	$42.32	8.287%	$45.8271	$45.83	$45.85	$45.80
Purchase #3	$98.56	11.168%	$109.5672	$109.57	$109.55	$109.60
Purchase #4	$13.98	4.293%	$14.5802	$14.58	$14.60	$14.60
Purchase #5	$139.50	11.708%	$155.8327	$155.83	$155.85	$155.80
Purchase #6	$239.82	5.729%	$253.5593	$253.56	$253.55	$253.60
Purchase #7	$101.56	10.703%	$112.43	$112.43	$112.45	$112.40
7 purchase totals =	$881.56		$967.9409	$967.94	$968.00	$967.90