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	$140.66	13.672%	$159.891	$159.89	$159.90	$159.90
Purchase #2	$79.45	13.608%	$90.2616	$90.26	$90.25	$90.30
Purchase #3	$118.27	13.211%	$133.8946	$133.89	$133.90	$133.90
Purchase #4	$113.29	3.867%	$117.6709	$117.67	$117.65	$117.70
Purchase #5	$232.31	4.804%	$243.4702	$243.47	$243.45	$243.50
Purchase #6	$225.62	13.259%	$255.535	$255.54	$255.55	$255.50
Purchase #7	$240.42	6.470%	$255.9752	$255.98	$256.00	$256.00
7 purchase totals =	$1,150.02		$1,256.6985	$1,256.70	$1,256.70	$1,256.80