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	$245.34	6.833%	$262.1041	$262.10	$262.10	$262.10
Purchase #2	$108.72	9.719%	$119.2865	$119.29	$119.30	$119.30
Purchase #3	$33.96	4.467%	$35.477	$35.48	$35.50	$35.50
Purchase #4	$74.37	5.411%	$78.3942	$78.39	$78.40	$78.40
Purchase #5	$62.85	13.168%	$71.1261	$71.13	$71.15	$71.10
Purchase #6	$44.80	11.458%	$49.9332	$49.93	$49.95	$49.90
Purchase #7	$146.60	6.168%	$155.6423	$155.64	$155.65	$155.60
7 purchase totals =	$716.64		$771.9634	$771.96	$772.05	$771.90