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	$73.34	7.439%	$78.7958	$78.80	$78.80	$78.80
Purchase #2	$44.41	8.225%	$48.0627	$48.06	$48.05	$48.10
Purchase #3	$68.97	6.339%	$73.342	$73.34	$73.35	$73.30
Purchase #4	$81.91	10.461%	$90.4786	$90.48	$90.50	$90.50
Purchase #5	$170.73	6.739%	$182.2355	$182.24	$182.25	$182.20
Purchase #6	$215.73	12.778%	$243.296	$243.30	$243.30	$243.30
Purchase #7	$108.30	3.836%	$112.4544	$112.45	$112.45	$112.50
7 purchase totals =	$763.39		$828.6650	$828.67	$828.70	$828.70