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	$17.59	5.732%	$18.5983	$18.60	$18.60	$18.60
Purchase #2	$28.85	12.783%	$32.5379	$32.54	$32.55	$32.50
Purchase #3	$12.31	8.153%	$13.3136	$13.31	$13.30	$13.30
Purchase #4	$234.67	11.641%	$261.9879	$261.99	$262.00	$262.00
Purchase #5	$54.80	13.180%	$62.0226	$62.02	$62.00	$62.00
Purchase #6	$145.30	11.823%	$162.4788	$162.48	$162.50	$162.50
Purchase #7	$36.67	10.341%	$40.462	$40.46	$40.45	$40.50
7 purchase totals =	$530.19		$591.4011	$591.40	$591.40	$591.40