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	$245.78	11.724%	$274.5952	$274.60	$274.60	$274.60
Purchase #2	$20.50	5.681%	$21.6646	$21.66	$21.65	$21.70
Purchase #3	$241.85	6.435%	$257.413	$257.41	$257.40	$257.40
Purchase #4	$6.42	12.649%	$7.2321	$7.23	$7.25	$7.20
Purchase #5	$101.52	9.854%	$111.5238	$111.52	$111.50	$111.50
Purchase #6	$95.70	4.568%	$100.0716	$100.07	$100.05	$100.10
Purchase #7	$79.27	3.277%	$81.8677	$81.87	$81.85	$81.90
7 purchase totals =	$791.04		$854.3680	$854.36	$854.30	$854.40