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	$140.74	12.523%	$158.3649	$158.36	$158.35	$158.40
Purchase #2	$157.54	3.286%	$162.7168	$162.72	$162.70	$162.70
Purchase #3	$66.65	7.756%	$71.8194	$71.82	$71.80	$71.80
Purchase #4	$49.27	13.192%	$55.7697	$55.77	$55.75	$55.80
Purchase #5	$240.94	13.565%	$273.6235	$273.62	$273.60	$273.60
Purchase #6	$138.91	4.129%	$144.6456	$144.65	$144.65	$144.60
Purchase #7	$96.29	7.649%	$103.6552	$103.66	$103.65	$103.70
7 purchase totals =	$890.34		$970.5951	$970.60	$970.50	$970.60