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	$53.85	9.751%	$59.1009	$59.10	$59.10	$59.10
Purchase #2	$116.58	9.211%	$127.3182	$127.32	$127.30	$127.30
Purchase #3	$66.47	8.508%	$72.1253	$72.13	$72.15	$72.10
Purchase #4	$140.77	8.810%	$153.1718	$153.17	$153.15	$153.20
Purchase #5	$56.72	10.192%	$62.5009	$62.50	$62.50	$62.50
Purchase #6	$67.93	11.695%	$75.8744	$75.87	$75.85	$75.90
Purchase #7	$127.64	5.246%	$134.336	$134.34	$134.35	$134.30
7 purchase totals =	$629.96		$684.4275	$684.43	$684.40	$684.40