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	$200.39	12.602%	$225.6431	$225.64	$225.65	$225.60
Purchase #2	$36.27	6.196%	$38.5173	$38.52	$38.50	$38.50
Purchase #3	$211.39	8.361%	$229.0643	$229.06	$229.05	$229.10
Purchase #4	$67.25	7.354%	$72.1956	$72.20	$72.20	$72.20
Purchase #5	$29.63	9.382%	$32.4099	$32.41	$32.40	$32.40
Purchase #6	$50.70	3.671%	$52.5612	$52.56	$52.55	$52.60
Purchase #7	$181.32	10.743%	$200.7992	$200.80	$200.80	$200.80
7 purchase totals =	$776.95		$851.1906	$851.19	$851.15	$851.20