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	$8.77	6.868%	$9.3723	$9.37	$9.35	$9.40
Purchase #2	$89.56	13.426%	$101.5843	$101.58	$101.60	$101.60
Purchase #3	$133.33	7.810%	$143.7431	$143.74	$143.75	$143.70
Purchase #4	$119.87	9.511%	$131.2708	$131.27	$131.25	$131.30
Purchase #5	$161.82	6.381%	$172.1457	$172.15	$172.15	$172.10
Purchase #6	$52.57	4.660%	$55.0198	$55.02	$55.00	$55.00
Purchase #7	$64.46	5.409%	$67.9466	$67.95	$67.95	$67.90
7 purchase totals =	$630.38		$681.0826	$681.08	$681.05	$681.00