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	$154.50	10.210%	$170.2745	$170.27	$170.25	$170.30
Purchase #2	$105.63	13.866%	$120.2767	$120.28	$120.30	$120.30
Purchase #3	$92.40	11.859%	$103.3577	$103.36	$103.35	$103.40
Purchase #4	$234.60	12.807%	$264.6452	$264.65	$264.65	$264.60
Purchase #5	$84.54	11.110%	$93.9324	$93.93	$93.95	$93.90
Purchase #6	$166.65	3.544%	$172.5561	$172.56	$172.55	$172.60
Purchase #7	$243.61	4.714%	$255.0938	$255.09	$255.10	$255.10
7 purchase totals =	$1,081.93		$1,180.1364	$1,180.14	$1,180.15	$1,180.20