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	$86.25	4.365%	$90.0148	$90.01	$90.00	$90.00
Purchase #2	$48.79	11.497%	$54.3994	$54.40	$54.40	$54.40
Purchase #3	$47.70	11.229%	$53.0562	$53.06	$53.05	$53.10
Purchase #4	$52.39	9.235%	$57.2282	$57.23	$57.25	$57.20
Purchase #5	$30.44	9.235%	$33.2511	$33.25	$33.25	$33.30
Purchase #6	$96.53	5.607%	$101.9424	$101.94	$101.95	$101.90
Purchase #7	$111.69	10.128%	$123.002	$123.00	$123.00	$123.00
7 purchase totals =	$473.79		$512.8941	$512.89	$512.90	$512.90