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	$90.64	6.577%	$96.6014	$96.60	$96.60	$96.60
Purchase #2	$63.68	13.762%	$72.4436	$72.44	$72.45	$72.40
Purchase #3	$109.25	3.159%	$112.7012	$112.70	$112.70	$112.70
Purchase #4	$141.67	12.489%	$159.3632	$159.36	$159.35	$159.40
Purchase #5	$28.65	12.567%	$32.2504	$32.25	$32.25	$32.30
Purchase #6	$136.53	8.578%	$148.2415	$148.24	$148.25	$148.20
Purchase #7	$153.99	8.184%	$166.5925	$166.59	$166.60	$166.60
7 purchase totals =	$724.41		$788.1938	$788.18	$788.20	$788.20