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	$137.90	3.446%	$142.652	$142.65	$142.65	$142.70
Purchase #2	$132.42	11.667%	$147.8694	$147.87	$147.85	$147.90
Purchase #3	$48.25	10.224%	$53.1831	$53.18	$53.20	$53.20
Purchase #4	$171.54	10.141%	$188.9359	$188.94	$188.95	$188.90
Purchase #5	$37.47	3.102%	$38.6323	$38.63	$38.65	$38.60
Purchase #6	$96.62	9.307%	$105.6124	$105.61	$105.60	$105.60
Purchase #7	$215.58	6.400%	$229.3771	$229.38	$229.40	$229.40
7 purchase totals =	$839.78		$906.2622	$906.26	$906.30	$906.30