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	$73.38	7.471%	$78.8622	$78.86	$78.85	$78.90
Purchase #2	$163.54	3.851%	$169.8379	$169.84	$169.85	$169.80
Purchase #3	$90.54	13.837%	$103.068	$103.07	$103.05	$103.10
Purchase #4	$142.52	4.105%	$148.3704	$148.37	$148.35	$148.40
Purchase #5	$171.32	6.723%	$182.8378	$182.84	$182.85	$182.80
Purchase #6	$64.42	13.657%	$73.2178	$73.22	$73.20	$73.20
Purchase #7	$66.42	12.533%	$74.7444	$74.74	$74.75	$74.70
7 purchase totals =	$772.14		$830.9385	$830.94	$830.90	$830.90