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	$134.27	8.490%	$145.6695	$145.67	$145.65	$145.70
Purchase #2	$84.36	6.350%	$89.7169	$89.72	$89.70	$89.70
Purchase #3	$27.63	12.245%	$31.0133	$31.01	$31.00	$31.00
Purchase #4	$216.54	12.158%	$242.8669	$242.87	$242.85	$242.90
Purchase #5	$45.74	11.847%	$51.1588	$51.16	$51.15	$51.20
Purchase #6	$206.41	10.197%	$227.4576	$227.46	$227.45	$227.50
Purchase #7	$155.86	5.681%	$164.7144	$164.71	$164.70	$164.70
7 purchase totals =	$870.81		$952.5974	$952.60	$952.50	$952.70