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	$85.56	6.206%	$90.8699	$90.87	$90.85	$90.90
Purchase #2	$83.50	10.521%	$92.285	$92.29	$92.30	$92.30
Purchase #3	$234.89	13.604%	$266.8444	$266.84	$266.85	$266.80
Purchase #4	$157.83	10.525%	$174.4416	$174.44	$174.45	$174.40
Purchase #5	$91.59	4.463%	$95.6777	$95.68	$95.70	$95.70
Purchase #6	$106.55	5.513%	$112.4241	$112.42	$112.40	$112.40
Purchase #7	$67.58	7.561%	$72.6897	$72.69	$72.70	$72.70
7 purchase totals =	$827.50		$905.2324	$905.23	$905.25	$905.20