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	$197.78	8.411%	$214.4153	$214.42	$214.40	$214.40
Purchase #2	$134.63	11.529%	$150.1515	$150.15	$150.15	$150.20
Purchase #3	$42.62	4.612%	$44.5856	$44.59	$44.60	$44.60
Purchase #4	$199.82	5.865%	$211.5394	$211.54	$211.55	$211.50
Purchase #5	$137.51	9.712%	$150.865	$150.87	$150.85	$150.90
Purchase #6	$133.84	5.188%	$140.7836	$140.78	$140.80	$140.80
Purchase #7	$51.51	11.120%	$57.2379	$57.24	$57.25	$57.20
7 purchase totals =	$897.71		$969.5783	$969.59	$969.60	$969.60