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	$104.68	9.716%	$114.8507	$114.85	$114.85	$114.90
Purchase #2	$42.58	7.497%	$45.7722	$45.77	$45.75	$45.80
Purchase #3	$234.65	10.406%	$259.0677	$259.07	$259.05	$259.10
Purchase #4	$208.57	7.139%	$223.4598	$223.46	$223.45	$223.50
Purchase #5	$50.50	9.770%	$55.4339	$55.43	$55.45	$55.40
Purchase #6	$99.52	8.393%	$107.8727	$107.87	$107.85	$107.90
Purchase #7	$30.94	7.435%	$33.2404	$33.24	$33.25	$33.20
7 purchase totals =	$771.44		$839.6974	$839.69	$839.65	$839.80