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	$68.38	6.469%	$72.8035	$72.80	$72.80	$72.80
Purchase #2	$222.90	6.533%	$237.4621	$237.46	$237.45	$237.50
Purchase #3	$73.62	9.128%	$80.34	$80.34	$80.35	$80.30
Purchase #4	$139.70	9.821%	$153.4199	$153.42	$153.40	$153.40
Purchase #5	$166.49	11.137%	$185.032	$185.03	$185.05	$185.00
Purchase #6	$118.93	13.226%	$134.6597	$134.66	$134.65	$134.70
Purchase #7	$40.50	4.441%	$42.2986	$42.30	$42.30	$42.30
7 purchase totals =	$830.52		$906.0158	$906.01	$906.00	$906.00