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	$99.54	9.625%	$109.1207	$109.12	$109.10	$109.10
Purchase #2	$31.33	10.190%	$34.5225	$34.52	$34.50	$34.50
Purchase #3	$132.75	8.696%	$144.2939	$144.29	$144.30	$144.30
Purchase #4	$163.98	8.729%	$178.2938	$178.29	$178.30	$178.30
Purchase #5	$95.98	13.137%	$108.5889	$108.59	$108.60	$108.60
Purchase #6	$36.97	13.337%	$41.9007	$41.90	$41.90	$41.90
Purchase #7	$173.69	13.117%	$196.4729	$196.47	$196.45	$196.50
7 purchase totals =	$734.24		$813.1934	$813.18	$813.15	$813.20