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	$52.80	12.768%	$59.5415	$59.54	$59.55	$59.50
Purchase #2	$19.41	10.330%	$21.4151	$21.42	$21.40	$21.40
Purchase #3	$34.90	12.136%	$39.1355	$39.14	$39.15	$39.10
Purchase #4	$151.56	6.718%	$161.7418	$161.74	$161.75	$161.70
Purchase #5	$12.75	13.599%	$14.4839	$14.48	$14.50	$14.50
Purchase #6	$71.82	7.732%	$77.3731	$77.37	$77.35	$77.40
Purchase #7	$208.83	13.394%	$236.8007	$236.80	$236.80	$236.80
7 purchase totals =	$552.07		$610.4916	$610.49	$610.50	$610.40