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	$75.46	10.702%	$83.5357	$83.54	$83.55	$83.50
Purchase #2	$126.65	11.323%	$140.9906	$140.99	$141.00	$141.00
Purchase #3	$231.95	10.199%	$255.6066	$255.61	$255.60	$255.60
Purchase #4	$27.82	12.866%	$31.3993	$31.40	$31.40	$31.40
Purchase #5	$152.91	3.527%	$158.3031	$158.30	$158.30	$158.30
Purchase #6	$33.71	11.551%	$37.6038	$37.60	$37.60	$37.60
Purchase #7	$70.73	4.658%	$74.0246	$74.02	$74.00	$74.00
7 purchase totals =	$719.23		$781.4637	$781.46	$781.45	$781.40