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	$245.61	4.212%	$255.9551	$255.96	$255.95	$256.00
Purchase #2	$53.76	12.534%	$60.4983	$60.50	$60.50	$60.50
Purchase #3	$85.72	10.675%	$94.8706	$94.87	$94.85	$94.90
Purchase #4	$195.94	13.536%	$222.4624	$222.46	$222.45	$222.50
Purchase #5	$57.87	4.405%	$60.4192	$60.42	$60.40	$60.40
Purchase #6	$229.39	3.521%	$237.4668	$237.47	$237.45	$237.50
Purchase #7	$135.56	8.624%	$147.2507	$147.25	$147.25	$147.30
7 purchase totals =	$1,003.85		$1,078.9231	$1,078.93	$1,078.85	$1,079.10