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	$35.75	7.839%	$38.5524	$38.55	$38.55	$38.60
Purchase #2	$200.80	6.286%	$213.4223	$213.42	$213.40	$213.40
Purchase #3	$106.83	6.219%	$113.4738	$113.47	$113.45	$113.50
Purchase #4	$38.43	13.243%	$43.5193	$43.52	$43.50	$43.50
Purchase #5	$73.38	12.383%	$82.4666	$82.47	$82.45	$82.50
Purchase #6	$146.47	9.232%	$159.9921	$159.99	$160.00	$160.00
Purchase #7	$39.45	9.112%	$43.0447	$43.04	$43.05	$43.00
7 purchase totals =	$641.11		$694.4712	$694.46	$694.40	$694.50