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	$57.87	11.452%	$64.4973	$64.50	$64.50	$64.50
Purchase #2	$238.54	5.307%	$251.1993	$251.20	$251.20	$251.20
Purchase #3	$153.65	9.795%	$168.7	$168.70	$168.70	$168.70
Purchase #4	$233.90	4.311%	$243.9834	$243.98	$244.00	$244.00
Purchase #5	$61.28	5.399%	$64.5885	$64.59	$64.60	$64.60
Purchase #6	$116.39	6.418%	$123.8599	$123.86	$123.85	$123.90
Purchase #7	$53.52	3.823%	$55.5661	$55.57	$55.55	$55.60
7 purchase totals =	$915.15		$972.3945	$972.40	$972.40	$972.50