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	$18.43	8.585%	$20.0122	$20.01	$20.00	$20.00
Purchase #2	$79.98	6.669%	$85.3139	$85.31	$85.30	$85.30
Purchase #3	$36.37	6.162%	$38.6111	$38.61	$38.60	$38.60
Purchase #4	$209.51	6.316%	$222.7427	$222.74	$222.75	$222.70
Purchase #5	$103.84	13.412%	$117.767	$117.77	$117.75	$117.80
Purchase #6	$231.43	11.186%	$257.3178	$257.32	$257.30	$257.30
Purchase #7	$47.90	12.534%	$53.9038	$53.90	$53.90	$53.90
7 purchase totals =	$727.46		$795.6685	$795.66	$795.60	$795.60