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	$40.64	6.665%	$43.3487	$43.35	$43.35	$43.30
Purchase #2	$13.68	9.501%	$14.9797	$14.98	$15.00	$15.00
Purchase #3	$6.53	11.282%	$7.2667	$7.27	$7.25	$7.30
Purchase #4	$139.52	9.340%	$152.5512	$152.55	$152.55	$152.60
Purchase #5	$75.52	12.740%	$85.1412	$85.14	$85.15	$85.10
Purchase #6	$87.58	13.551%	$99.448	$99.45	$99.45	$99.40
Purchase #7	$15.89	3.757%	$16.487	$16.49	$16.50	$16.50
7 purchase totals =	$379.36		$419.2225	$419.23	$419.25	$419.20