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	$96.73	7.326%	$103.8164	$103.82	$103.80	$103.80
Purchase #2	$86.27	13.461%	$97.8828	$97.88	$97.90	$97.90
Purchase #3	$104.63	6.534%	$111.4665	$111.47	$111.45	$111.50
Purchase #4	$45.64	9.596%	$50.0196	$50.02	$50.00	$50.00
Purchase #5	$28.58	11.712%	$31.9273	$31.93	$31.95	$31.90
Purchase #6	$115.32	6.529%	$122.8492	$122.85	$122.85	$122.80
Purchase #7	$172.74	10.411%	$190.724	$190.72	$190.70	$190.70
7 purchase totals =	$649.91		$708.6858	$708.69	$708.65	$708.60