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	$50.59	13.662%	$57.5016	$57.50	$57.50	$57.50
Purchase #2	$123.68	10.679%	$136.8878	$136.89	$136.90	$136.90
Purchase #3	$68.77	6.379%	$73.1568	$73.16	$73.15	$73.20
Purchase #4	$203.58	6.620%	$217.057	$217.06	$217.05	$217.10
Purchase #5	$89.64	7.789%	$96.6221	$96.62	$96.60	$96.60
Purchase #6	$148.69	10.772%	$164.7069	$164.71	$164.70	$164.70
Purchase #7	$59.83	13.520%	$67.919	$67.92	$67.90	$67.90
7 purchase totals =	$744.78		$813.8512	$813.86	$813.80	$813.90