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	$155.42	10.434%	$171.6365	$171.64	$171.65	$171.60
Purchase #2	$74.40	12.190%	$83.4694	$83.47	$83.45	$83.50
Purchase #3	$197.45	12.325%	$221.7857	$221.79	$221.80	$221.80
Purchase #4	$98.76	6.395%	$105.0757	$105.08	$105.10	$105.10
Purchase #5	$31.34	4.774%	$32.8362	$32.84	$32.85	$32.80
Purchase #6	$98.50	3.583%	$102.0293	$102.03	$102.05	$102.00
Purchase #7	$48.88	11.388%	$54.4465	$54.45	$54.45	$54.40
7 purchase totals =	$704.75		$771.2793	$771.30	$771.35	$771.20