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	$134.88	5.628%	$142.471	$142.47	$142.45	$142.50
Purchase #2	$48.78	11.407%	$54.3443	$54.34	$54.35	$54.30
Purchase #3	$52.44	9.554%	$57.4501	$57.45	$57.45	$57.50
Purchase #4	$70.89	13.689%	$80.5941	$80.59	$80.60	$80.60
Purchase #5	$170.76	5.189%	$179.6207	$179.62	$179.60	$179.60
Purchase #6	$214.76	13.244%	$243.2028	$243.20	$243.20	$243.20
Purchase #7	$176.65	12.817%	$199.2912	$199.29	$199.30	$199.30
7 purchase totals =	$869.16		$956.9742	$956.96	$956.95	$957.00