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	$144.59	8.257%	$156.5288	$156.53	$156.55	$156.50
Purchase #2	$201.99	10.594%	$223.3888	$223.39	$223.40	$223.40
Purchase #3	$116.80	5.706%	$123.4646	$123.46	$123.45	$123.50
Purchase #4	$203.83	11.425%	$227.1176	$227.12	$227.10	$227.10
Purchase #5	$227.99	12.212%	$255.8321	$255.83	$255.85	$255.80
Purchase #6	$153.59	4.398%	$160.3449	$160.34	$160.35	$160.30
Purchase #7	$166.80	10.688%	$184.6276	$184.63	$184.65	$184.60
7 purchase totals =	$1,215.59		$1,331.3044	$1,331.30	$1,331.35	$1,331.20