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	$72.95	11.157%	$81.089	$81.09	$81.10	$81.10
Purchase #2	$96.59	12.686%	$108.8434	$108.84	$108.85	$108.80
Purchase #3	$56.89	4.540%	$59.4728	$59.47	$59.45	$59.50
Purchase #4	$78.88	13.513%	$89.5391	$89.54	$89.55	$89.50
Purchase #5	$146.46	7.399%	$157.2966	$157.30	$157.30	$157.30
Purchase #6	$238.86	13.626%	$271.4071	$271.41	$271.40	$271.40
Purchase #7	$175.35	9.259%	$191.5857	$191.59	$191.60	$191.60
7 purchase totals =	$865.98		$959.2337	$959.24	$959.25	$959.20