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	$203.65	13.330%	$230.7965	$230.80	$230.80	$230.80
Purchase #2	$117.30	5.290%	$123.5052	$123.51	$123.50	$123.50
Purchase #3	$147.32	9.779%	$161.7264	$161.73	$161.75	$161.70
Purchase #4	$143.43	6.554%	$152.8304	$152.83	$152.85	$152.80
Purchase #5	$6.30	12.773%	$7.1047	$7.10	$7.10	$7.10
Purchase #6	$53.96	10.255%	$59.4936	$59.49	$59.50	$59.50
Purchase #7	$35.48	5.496%	$37.43	$37.43	$37.45	$37.40
7 purchase totals =	$707.44		$772.8868	$772.89	$772.95	$772.80