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	$138.64	9.504%	$151.8163	$151.82	$151.80	$151.80
Purchase #2	$34.72	3.682%	$35.9984	$36.00	$36.00	$36.00
Purchase #3	$31.55	12.529%	$35.5029	$35.50	$35.50	$35.50
Purchase #4	$122.69	3.801%	$127.3534	$127.35	$127.35	$127.40
Purchase #5	$238.37	6.386%	$253.5923	$253.59	$253.60	$253.60
Purchase #6	$45.70	6.591%	$48.7121	$48.71	$48.70	$48.70
Purchase #7	$223.85	5.618%	$236.4259	$236.43	$236.45	$236.40
7 purchase totals =	$835.52		$889.4013	$889.40	$889.40	$889.40