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	$238.57	13.827%	$271.5571	$271.56	$271.55	$271.60
Purchase #2	$240.95	12.533%	$271.1483	$271.15	$271.15	$271.10
Purchase #3	$123.75	3.165%	$127.6667	$127.67	$127.65	$127.70
Purchase #4	$33.61	3.858%	$34.9067	$34.91	$34.90	$34.90
Purchase #5	$65.29	7.600%	$70.252	$70.25	$70.25	$70.30
Purchase #6	$211.26	3.268%	$218.164	$218.16	$218.15	$218.20
Purchase #7	$56.59	11.761%	$63.2455	$63.25	$63.25	$63.20
7 purchase totals =	$970.02		$1,056.9403	$1,056.95	$1,056.90	$1,057.00