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	$72.39	9.138%	$79.005	$79.01	$79.00	$79.00
Purchase #2	$34.81	10.146%	$38.3418	$38.34	$38.35	$38.30
Purchase #3	$67.72	6.337%	$72.0114	$72.01	$72.00	$72.00
Purchase #4	$117.45	9.682%	$128.8215	$128.82	$128.80	$128.80
Purchase #5	$127.57	5.754%	$134.9104	$134.91	$134.90	$134.90
Purchase #6	$168.78	3.467%	$174.6316	$174.63	$174.65	$174.60
Purchase #7	$129.42	12.329%	$145.3762	$145.38	$145.40	$145.40
7 purchase totals =	$718.14		$773.0979	$773.10	$773.10	$773.00