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	$250.86	11.863%	$280.6195	$280.62	$280.60	$280.60
Purchase #2	$33.35	7.469%	$35.8409	$35.84	$35.85	$35.80
Purchase #3	$127.38	4.771%	$133.4573	$133.46	$133.45	$133.50
Purchase #4	$238.97	10.288%	$263.5552	$263.56	$263.55	$263.60
Purchase #5	$62.87	11.391%	$70.0315	$70.03	$70.05	$70.00
Purchase #6	$48.81	11.381%	$54.3651	$54.37	$54.35	$54.40
Purchase #7	$174.94	5.376%	$184.3448	$184.34	$184.35	$184.30
7 purchase totals =	$937.18		$1,022.2143	$1,022.22	$1,022.20	$1,022.20