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	$203.81	10.560%	$225.3323	$225.33	$225.35	$225.30
Purchase #2	$56.69	5.539%	$59.8301	$59.83	$59.85	$59.80
Purchase #3	$158.60	13.346%	$179.7668	$179.77	$179.75	$179.80
Purchase #4	$155.46	7.699%	$167.4289	$167.43	$167.45	$167.40
Purchase #5	$198.92	9.184%	$217.1888	$217.19	$217.20	$217.20
Purchase #6	$65.63	11.683%	$73.2976	$73.30	$73.30	$73.30
Purchase #7	$69.47	11.488%	$77.4507	$77.45	$77.45	$77.50
7 purchase totals =	$908.58		$1,000.2952	$1,000.30	$1,000.35	$1,000.30