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	$19.85	5.821%	$21.0055	$21.01	$21.00	$21.00
Purchase #2	$122.42	13.297%	$138.6982	$138.70	$138.70	$138.70
Purchase #3	$155.32	8.623%	$168.7132	$168.71	$168.70	$168.70
Purchase #4	$132.32	13.719%	$150.473	$150.47	$150.45	$150.50
Purchase #5	$76.54	13.161%	$86.6134	$86.61	$86.60	$86.60
Purchase #6	$240.62	5.287%	$253.3416	$253.34	$253.35	$253.30
Purchase #7	$217.36	11.829%	$243.0715	$243.07	$243.05	$243.10
7 purchase totals =	$964.43		$1,061.9164	$1,061.91	$1,061.85	$1,061.90