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	$74.64	8.107%	$80.6911	$80.69	$80.70	$80.70
Purchase #2	$140.69	11.188%	$156.4304	$156.43	$156.45	$156.40
Purchase #3	$165.35	6.797%	$176.5888	$176.59	$176.60	$176.60
Purchase #4	$221.95	9.660%	$243.3904	$243.39	$243.40	$243.40
Purchase #5	$63.68	13.120%	$72.0348	$72.03	$72.05	$72.00
Purchase #6	$215.82	11.102%	$239.7803	$239.78	$239.80	$239.80
Purchase #7	$238.64	6.849%	$254.9845	$254.98	$255.00	$255.00
7 purchase totals =	$1,120.77		$1,223.9003	$1,223.89	$1,224.00	$1,223.90