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	$80.31	12.562%	$90.3985	$90.40	$90.40	$90.40
Purchase #2	$191.53	12.433%	$215.3429	$215.34	$215.35	$215.30
Purchase #3	$120.85	13.703%	$137.4101	$137.41	$137.40	$137.40
Purchase #4	$96.58	8.725%	$105.0066	$105.01	$105.00	$105.00
Purchase #5	$244.62	4.501%	$255.6303	$255.63	$255.65	$255.60
Purchase #6	$170.53	7.488%	$183.2993	$183.30	$183.30	$183.30
Purchase #7	$176.81	8.277%	$191.4446	$191.44	$191.45	$191.40
7 purchase totals =	$1,081.23		$1,178.5323	$1,178.53	$1,178.55	$1,178.40