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	$249.29	9.748%	$273.5908	$273.59	$273.60	$273.60
Purchase #2	$224.78	10.777%	$249.0045	$249.00	$249.00	$249.00
Purchase #3	$150.97	10.591%	$166.9592	$166.96	$166.95	$167.00
Purchase #4	$60.25	11.217%	$67.0082	$67.01	$67.00	$67.00
Purchase #5	$107.76	7.753%	$116.1146	$116.11	$116.10	$116.10
Purchase #6	$103.30	7.832%	$111.3905	$111.39	$111.40	$111.40
Purchase #7	$153.34	9.578%	$168.0269	$168.03	$168.05	$168.00
7 purchase totals =	$1,049.69		$1,152.0947	$1,152.09	$1,152.10	$1,152.10