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	$168.38	5.596%	$177.8025	$177.80	$177.80	$177.80
Purchase #2	$67.57	11.792%	$75.5379	$75.54	$75.55	$75.50
Purchase #3	$64.60	3.139%	$66.6278	$66.63	$66.65	$66.60
Purchase #4	$142.63	6.225%	$151.5087	$151.51	$151.50	$151.50
Purchase #5	$51.55	5.233%	$54.2476	$54.25	$54.25	$54.20
Purchase #6	$67.77	6.538%	$72.2008	$72.20	$72.20	$72.20
Purchase #7	$222.36	13.147%	$251.5937	$251.59	$251.60	$251.60
7 purchase totals =	$784.86		$849.5190	$849.52	$849.55	$849.40