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	$36.85	12.635%	$41.506	$41.51	$41.50	$41.50
Purchase #2	$210.77	8.802%	$229.322	$229.32	$229.30	$229.30
Purchase #3	$204.80	6.144%	$217.3829	$217.38	$217.40	$217.40
Purchase #4	$63.47	7.395%	$68.1636	$68.16	$68.15	$68.20
Purchase #5	$94.28	10.216%	$103.9116	$103.91	$103.90	$103.90
Purchase #6	$50.49	6.117%	$53.5785	$53.58	$53.60	$53.60
Purchase #7	$100.82	8.737%	$109.6286	$109.63	$109.65	$109.60
7 purchase totals =	$761.48		$823.4932	$823.49	$823.50	$823.50