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	$166.80	13.128%	$188.6975	$188.70	$188.70	$188.70
Purchase #2	$99.34	4.643%	$103.9524	$103.95	$103.95	$104.00
Purchase #3	$221.86	4.365%	$231.5442	$231.54	$231.55	$231.50
Purchase #4	$193.89	11.830%	$216.8272	$216.83	$216.85	$216.80
Purchase #5	$178.45	5.762%	$188.7323	$188.73	$188.75	$188.70
Purchase #6	$65.45	10.810%	$72.5251	$72.53	$72.55	$72.50
Purchase #7	$123.90	5.361%	$130.5423	$130.54	$130.55	$130.50
7 purchase totals =	$1,049.69		$1,132.8210	$1,132.82	$1,132.90	$1,132.70