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	$97.72	3.183%	$100.8304	$100.83	$100.85	$100.80
Purchase #2	$248.41	12.439%	$279.3097	$279.31	$279.30	$279.30
Purchase #3	$189.60	8.766%	$206.2203	$206.22	$206.20	$206.20
Purchase #4	$229.97	13.358%	$260.6894	$260.69	$260.70	$260.70
Purchase #5	$43.59	5.462%	$45.9709	$45.97	$45.95	$46.00
Purchase #6	$99.27	5.194%	$104.4261	$104.43	$104.45	$104.40
Purchase #7	$237.37	13.555%	$269.5455	$269.55	$269.55	$269.50
7 purchase totals =	$1,145.93		$1,266.9923	$1,267.00	$1,267.00	$1,266.90