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	$249.64	3.854%	$259.2611	$259.26	$259.25	$259.30
Purchase #2	$51.79	13.868%	$58.9722	$58.97	$58.95	$59.00
Purchase #3	$148.75	13.328%	$168.5754	$168.58	$168.60	$168.60
Purchase #4	$20.27	7.723%	$21.8355	$21.84	$21.85	$21.80
Purchase #5	$66.52	6.871%	$71.0906	$71.09	$71.10	$71.10
Purchase #6	$158.33	4.690%	$165.7557	$165.76	$165.75	$165.80
Purchase #7	$33.87	13.819%	$38.5505	$38.55	$38.55	$38.60
7 purchase totals =	$729.17		$784.0410	$784.05	$784.05	$784.20