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	$73.80	6.849%	$78.8546	$78.85	$78.85	$78.90
Purchase #2	$126.55	10.584%	$139.9441	$139.94	$139.95	$139.90
Purchase #3	$131.33	12.783%	$148.1179	$148.12	$148.10	$148.10
Purchase #4	$67.29	11.485%	$75.0183	$75.02	$75.00	$75.00
Purchase #5	$235.27	8.643%	$255.6044	$255.60	$255.60	$255.60
Purchase #6	$120.59	6.682%	$128.6478	$128.65	$128.65	$128.60
Purchase #7	$195.25	10.369%	$215.4955	$215.50	$215.50	$215.50
7 purchase totals =	$950.08		$1,041.6826	$1,041.68	$1,041.65	$1,041.60