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	$98.42	4.698%	$103.0438	$103.04	$103.05	$103.00
Purchase #2	$163.95	13.338%	$185.8177	$185.82	$185.80	$185.80
Purchase #3	$185.29	8.241%	$200.5597	$200.56	$200.55	$200.60
Purchase #4	$145.46	5.634%	$153.6552	$153.66	$153.65	$153.70
Purchase #5	$185.88	3.581%	$192.5364	$192.54	$192.55	$192.50
Purchase #6	$213.99	12.801%	$241.3829	$241.38	$241.40	$241.40
Purchase #7	$139.59	12.192%	$156.6088	$156.61	$156.60	$156.60
7 purchase totals =	$1,132.58		$1,233.6045	$1,233.61	$1,233.60	$1,233.60