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	$19.56	12.774%	$22.0586	$22.06	$22.05	$22.10
Purchase #2	$228.45	12.846%	$257.7967	$257.80	$257.80	$257.80
Purchase #3	$189.56	10.533%	$209.5264	$209.53	$209.55	$209.50
Purchase #4	$85.74	11.500%	$95.6001	$95.60	$95.60	$95.60
Purchase #5	$52.82	8.585%	$57.3546	$57.35	$57.35	$57.40
Purchase #6	$168.51	10.262%	$185.8025	$185.80	$185.80	$185.80
Purchase #7	$131.25	8.451%	$142.3419	$142.34	$142.35	$142.30
7 purchase totals =	$875.89		$970.4808	$970.48	$970.50	$970.50