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	$143.47	8.734%	$156.0007	$156.00	$156.00	$156.00
Purchase #2	$143.90	3.450%	$148.8646	$148.86	$148.85	$148.90
Purchase #3	$130.86	10.639%	$144.7822	$144.78	$144.80	$144.80
Purchase #4	$65.30	11.234%	$72.6358	$72.64	$72.65	$72.60
Purchase #5	$161.32	11.131%	$179.2765	$179.28	$179.30	$179.30
Purchase #6	$73.95	5.772%	$78.2184	$78.22	$78.20	$78.20
Purchase #7	$23.97	11.124%	$26.6364	$26.64	$26.65	$26.60
7 purchase totals =	$742.77		$806.4146	$806.42	$806.45	$806.40