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	$17.97	3.520%	$18.6025	$18.60	$18.60	$18.60
Purchase #2	$184.35	6.561%	$196.4452	$196.45	$196.45	$196.40
Purchase #3	$65.34	3.252%	$67.4649	$67.46	$67.45	$67.50
Purchase #4	$47.59	8.323%	$51.5509	$51.55	$51.55	$51.60
Purchase #5	$15.43	3.561%	$15.9795	$15.98	$16.00	$16.00
Purchase #6	$96.53	13.424%	$109.4882	$109.49	$109.50	$109.50
Purchase #7	$85.54	3.598%	$88.6177	$88.62	$88.60	$88.60
7 purchase totals =	$512.75		$548.1489	$548.15	$548.15	$548.20