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	$30.52	12.797%	$34.4256	$34.43	$34.45	$34.40
Purchase #2	$233.33	5.227%	$245.5262	$245.53	$245.55	$245.50
Purchase #3	$155.77	12.807%	$175.7195	$175.72	$175.70	$175.70
Purchase #4	$66.47	7.706%	$71.5922	$71.59	$71.60	$71.60
Purchase #5	$115.40	3.711%	$119.6825	$119.68	$119.70	$119.70
Purchase #6	$54.85	11.293%	$61.0442	$61.04	$61.05	$61.00
Purchase #7	$228.43	6.170%	$242.5241	$242.52	$242.50	$242.50
7 purchase totals =	$884.77		$950.5143	$950.51	$950.55	$950.40