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	$73.48	6.746%	$78.437	$78.44	$78.45	$78.40
Purchase #2	$46.30	9.679%	$50.7814	$50.78	$50.80	$50.80
Purchase #3	$224.45	8.611%	$243.7774	$243.78	$243.80	$243.80
Purchase #4	$75.45	7.584%	$81.1721	$81.17	$81.15	$81.20
Purchase #5	$105.54	11.418%	$117.5906	$117.59	$117.60	$117.60
Purchase #6	$59.61	5.439%	$62.8522	$62.85	$62.85	$62.90
Purchase #7	$49.43	7.114%	$52.9465	$52.95	$52.95	$52.90
7 purchase totals =	$634.26		$687.5572	$687.56	$687.60	$687.60