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	$154.73	7.403%	$166.1847	$166.18	$166.20	$166.20
Purchase #2	$74.50	5.601%	$78.6727	$78.67	$78.65	$78.70
Purchase #3	$28.42	5.254%	$29.9132	$29.91	$29.90	$29.90
Purchase #4	$40.91	10.192%	$45.0795	$45.08	$45.10	$45.10
Purchase #5	$222.51	5.197%	$234.0738	$234.07	$234.05	$234.10
Purchase #6	$107.28	3.361%	$110.8857	$110.89	$110.90	$110.90
Purchase #7	$41.86	8.754%	$45.5244	$45.52	$45.50	$45.50
7 purchase totals =	$670.21		$710.3340	$710.32	$710.30	$710.40