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	$85.94	4.574%	$89.8709	$89.87	$89.85	$89.90
Purchase #2	$153.47	12.615%	$172.8302	$172.83	$172.85	$172.80
Purchase #3	$242.64	11.632%	$270.8639	$270.86	$270.85	$270.90
Purchase #4	$52.28	6.395%	$55.6233	$55.62	$55.60	$55.60
Purchase #5	$121.74	11.583%	$135.8411	$135.84	$135.85	$135.80
Purchase #6	$158.47	3.480%	$163.9848	$163.98	$164.00	$164.00
Purchase #7	$153.47	5.259%	$161.541	$161.54	$161.55	$161.50
7 purchase totals =	$968.01		$1,050.5552	$1,050.54	$1,050.55	$1,050.50