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	$51.90	9.402%	$56.7796	$56.78	$56.80	$56.80
Purchase #2	$192.38	9.737%	$211.112	$211.11	$211.10	$211.10
Purchase #3	$43.61	5.225%	$45.8886	$45.89	$45.90	$45.90
Purchase #4	$163.48	11.595%	$182.4355	$182.44	$182.45	$182.40
Purchase #5	$93.87	10.431%	$103.6616	$103.66	$103.65	$103.70
Purchase #6	$115.62	4.290%	$120.5801	$120.58	$120.60	$120.60
Purchase #7	$78.39	3.789%	$81.3602	$81.36	$81.35	$81.40
7 purchase totals =	$739.25		$801.8176	$801.82	$801.85	$801.90