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	$138.67	7.222%	$148.6847	$148.68	$148.70	$148.70
Purchase #2	$246.28	9.705%	$270.1815	$270.18	$270.20	$270.20
Purchase #3	$25.32	13.848%	$28.8263	$28.83	$28.85	$28.80
Purchase #4	$85.53	4.147%	$89.0769	$89.08	$89.10	$89.10
Purchase #5	$38.53	11.555%	$42.9821	$42.98	$43.00	$43.00
Purchase #6	$153.31	8.118%	$165.7557	$165.76	$165.75	$165.80
Purchase #7	$92.82	13.463%	$105.3164	$105.32	$105.30	$105.30
7 purchase totals =	$780.46		$850.8236	$850.83	$850.90	$850.90