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	$55.26	10.451%	$61.0352	$61.04	$61.05	$61.00
Purchase #2	$109.50	6.219%	$116.3098	$116.31	$116.30	$116.30
Purchase #3	$85.77	11.197%	$95.3737	$95.37	$95.35	$95.40
Purchase #4	$172.35	5.341%	$181.5552	$181.56	$181.55	$181.60
Purchase #5	$52.36	7.590%	$56.3341	$56.33	$56.35	$56.30
Purchase #6	$60.43	3.720%	$62.678	$62.68	$62.70	$62.70
Purchase #7	$60.69	9.759%	$66.6127	$66.61	$66.60	$66.60
7 purchase totals =	$596.36		$639.8987	$639.90	$639.90	$639.90