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	$239.35	8.501%	$259.6971	$259.70	$259.70	$259.70
Purchase #2	$205.76	10.799%	$227.98	$227.98	$228.00	$228.00
Purchase #3	$85.96	4.791%	$90.0783	$90.08	$90.10	$90.10
Purchase #4	$217.89	6.618%	$232.31	$232.31	$232.30	$232.30
Purchase #5	$205.82	8.154%	$222.6026	$222.60	$222.60	$222.60
Purchase #6	$164.46	8.400%	$178.2746	$178.27	$178.25	$178.30
Purchase #7	$79.58	7.496%	$85.5453	$85.55	$85.55	$85.50
7 purchase totals =	$1,198.82		$1,296.4879	$1,296.49	$1,296.50	$1,296.50