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	$223.85	6.739%	$238.9353	$238.94	$238.95	$238.90
Purchase #2	$134.59	4.737%	$140.9655	$140.97	$140.95	$141.00
Purchase #3	$97.32	8.293%	$105.3907	$105.39	$105.40	$105.40
Purchase #4	$50.45	10.621%	$55.8083	$55.81	$55.80	$55.80
Purchase #5	$54.63	13.379%	$61.9389	$61.94	$61.95	$61.90
Purchase #6	$139.91	3.611%	$144.9622	$144.96	$144.95	$145.00
Purchase #7	$163.56	6.334%	$173.9199	$173.92	$173.90	$173.90
7 purchase totals =	$864.31		$921.9208	$921.93	$921.90	$921.90