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	$76.95	10.627%	$85.1275	$85.13	$85.15	$85.10
Purchase #2	$174.97	12.747%	$197.2734	$197.27	$197.25	$197.30
Purchase #3	$134.85	3.630%	$139.7451	$139.75	$139.75	$139.70
Purchase #4	$240.75	6.463%	$256.3097	$256.31	$256.30	$256.30
Purchase #5	$92.76	11.623%	$103.5415	$103.54	$103.55	$103.50
Purchase #6	$34.72	10.218%	$38.2677	$38.27	$38.25	$38.30
Purchase #7	$237.32	13.476%	$269.3012	$269.30	$269.30	$269.30
7 purchase totals =	$992.32		$1,089.5661	$1,089.57	$1,089.55	$1,089.50