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	$100.56	10.786%	$111.4064	$111.41	$111.40	$111.40
Purchase #2	$229.47	12.460%	$258.062	$258.06	$258.05	$258.10
Purchase #3	$21.93	8.560%	$23.8072	$23.81	$23.80	$23.80
Purchase #4	$103.68	13.862%	$118.0521	$118.05	$118.05	$118.10
Purchase #5	$57.48	12.118%	$64.4454	$64.45	$64.45	$64.40
Purchase #6	$133.32	4.668%	$139.5434	$139.54	$139.55	$139.50
Purchase #7	$83.61	9.667%	$91.6926	$91.69	$91.70	$91.70
7 purchase totals =	$730.05		$807.0091	$807.01	$807.00	$807.00