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	$136.71	10.862%	$151.5594	$151.56	$151.55	$151.60
Purchase #2	$163.65	5.264%	$172.2645	$172.26	$172.25	$172.30
Purchase #3	$43.32	9.805%	$47.5675	$47.57	$47.55	$47.60
Purchase #4	$103.66	4.205%	$108.0189	$108.02	$108.00	$108.00
Purchase #5	$239.80	6.139%	$254.5213	$254.52	$254.50	$254.50
Purchase #6	$159.59	12.125%	$178.9403	$178.94	$178.95	$178.90
Purchase #7	$37.94	12.309%	$42.61	$42.61	$42.60	$42.60
7 purchase totals =	$884.67		$955.4819	$955.48	$955.40	$955.50