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	$49.71	8.872%	$54.1203	$54.12	$54.10	$54.10
Purchase #2	$185.35	5.114%	$194.8288	$194.83	$194.85	$194.80
Purchase #3	$92.79	7.832%	$100.0573	$100.06	$100.05	$100.10
Purchase #4	$207.39	7.289%	$222.5067	$222.51	$222.50	$222.50
Purchase #5	$6.55	4.274%	$6.8299	$6.83	$6.85	$6.80
Purchase #6	$171.92	11.564%	$191.8008	$191.80	$191.80	$191.80
Purchase #7	$42.86	13.630%	$48.7018	$48.70	$48.70	$48.70
7 purchase totals =	$756.57		$818.8456	$818.85	$818.85	$818.80