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	$172.80	6.372%	$183.8108	$183.81	$183.80	$183.80
Purchase #2	$85.32	5.583%	$90.0834	$90.08	$90.10	$90.10
Purchase #3	$234.77	9.780%	$257.7305	$257.73	$257.75	$257.70
Purchase #4	$57.46	4.827%	$60.2336	$60.23	$60.25	$60.20
Purchase #5	$128.55	10.508%	$142.058	$142.06	$142.05	$142.10
Purchase #6	$231.98	4.466%	$242.3402	$242.34	$242.35	$242.30
Purchase #7	$33.83	4.847%	$35.4697	$35.47	$35.45	$35.50
7 purchase totals =	$944.71		$1,011.7262	$1,011.72	$1,011.75	$1,011.70