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	$55.79	12.553%	$62.7933	$62.79	$62.80	$62.80
Purchase #2	$39.76	11.705%	$44.4139	$44.41	$44.40	$44.40
Purchase #3	$94.85	11.179%	$105.4533	$105.45	$105.45	$105.50
Purchase #4	$110.62	7.850%	$119.3037	$119.30	$119.30	$119.30
Purchase #5	$123.44	3.339%	$127.5617	$127.56	$127.55	$127.60
Purchase #6	$107.54	5.862%	$113.844	$113.84	$113.85	$113.80
Purchase #7	$58.64	7.562%	$63.0744	$63.07	$63.05	$63.10
7 purchase totals =	$590.64		$636.4443	$636.42	$636.40	$636.50