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	$17.66	13.461%	$20.0372	$20.04	$20.05	$20.00
Purchase #2	$59.98	10.453%	$66.2497	$66.25	$66.25	$66.20
Purchase #3	$133.57	12.782%	$150.6429	$150.64	$150.65	$150.60
Purchase #4	$120.92	12.510%	$136.0471	$136.05	$136.05	$136.00
Purchase #5	$241.69	9.671%	$265.0638	$265.06	$265.05	$265.10
Purchase #6	$176.33	11.398%	$196.4281	$196.43	$196.45	$196.40
Purchase #7	$33.46	9.330%	$36.5818	$36.58	$36.60	$36.60
7 purchase totals =	$783.61		$871.0506	$871.05	$871.10	$870.90