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	$66.70	4.176%	$69.4854	$69.49	$69.50	$69.50
Purchase #2	$62.29	7.649%	$67.0546	$67.05	$67.05	$67.10
Purchase #3	$53.42	6.784%	$57.044	$57.04	$57.05	$57.00
Purchase #4	$148.64	11.705%	$166.0383	$166.04	$166.05	$166.00
Purchase #5	$72.89	7.556%	$78.3976	$78.40	$78.40	$78.40
Purchase #6	$54.39	4.115%	$56.6281	$56.63	$56.65	$56.60
Purchase #7	$22.38	12.762%	$25.2361	$25.24	$25.25	$25.20
7 purchase totals =	$480.71		$519.8841	$519.89	$519.95	$519.80