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	$50.71	12.123%	$56.8576	$56.86	$56.85	$56.90
Purchase #2	$99.82	8.178%	$107.9833	$107.98	$108.00	$108.00
Purchase #3	$191.61	11.554%	$213.7486	$213.75	$213.75	$213.70
Purchase #4	$174.52	6.418%	$185.7207	$185.72	$185.70	$185.70
Purchase #5	$74.50	8.563%	$80.8794	$80.88	$80.90	$80.90
Purchase #6	$238.25	12.412%	$267.8216	$267.82	$267.80	$267.80
Purchase #7	$95.67	9.386%	$104.6496	$104.65	$104.65	$104.60
7 purchase totals =	$925.08		$1,017.6608	$1,017.66	$1,017.65	$1,017.60