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	$56.43	9.508%	$61.7954	$61.80	$61.80	$61.80
Purchase #2	$96.74	4.289%	$100.8892	$100.89	$100.90	$100.90
Purchase #3	$50.68	9.371%	$55.4292	$55.43	$55.45	$55.40
Purchase #4	$165.56	4.525%	$173.0516	$173.05	$173.05	$173.10
Purchase #5	$114.53	12.485%	$128.8291	$128.83	$128.85	$128.80
Purchase #6	$111.91	4.435%	$116.8732	$116.87	$116.85	$116.90
Purchase #7	$32.41	11.287%	$36.0681	$36.07	$36.05	$36.10
7 purchase totals =	$628.26		$672.9358	$672.94	$672.95	$673.00