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	$159.27	9.314%	$174.1044	$174.10	$174.10	$174.10
Purchase #2	$220.33	4.832%	$230.9763	$230.98	$231.00	$231.00
Purchase #3	$231.62	10.265%	$255.3958	$255.40	$255.40	$255.40
Purchase #4	$35.34	13.635%	$40.1586	$40.16	$40.15	$40.20
Purchase #5	$103.84	7.673%	$111.8076	$111.81	$111.80	$111.80
Purchase #6	$6.82	11.834%	$7.6271	$7.63	$7.65	$7.60
Purchase #7	$36.68	4.237%	$38.2341	$38.23	$38.25	$38.20
7 purchase totals =	$793.90		$858.3039	$858.31	$858.35	$858.30