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	$240.72	13.527%	$273.2822	$273.28	$273.30	$273.30
Purchase #2	$120.36	13.367%	$136.4485	$136.45	$136.45	$136.40
Purchase #3	$151.61	13.449%	$172	$172.00	$172.00	$172.00
Purchase #4	$5.27	7.202%	$5.6495	$5.65	$5.65	$5.60
Purchase #5	$190.47	5.251%	$200.4716	$200.47	$200.45	$200.50
Purchase #6	$140.94	8.455%	$152.8565	$152.86	$152.85	$152.90
Purchase #7	$174.69	12.329%	$196.2275	$196.23	$196.25	$196.20
7 purchase totals =	$1,024.06		$1,136.9358	$1,136.94	$1,136.95	$1,136.90