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	$170.91	12.323%	$191.9712	$191.97	$191.95	$192.00
Purchase #2	$191.40	12.527%	$215.3767	$215.38	$215.40	$215.40
Purchase #3	$217.50	3.559%	$225.2408	$225.24	$225.25	$225.20
Purchase #4	$36.45	8.679%	$39.6135	$39.61	$39.60	$39.60
Purchase #5	$19.25	9.786%	$21.1338	$21.13	$21.15	$21.10
Purchase #6	$96.80	12.429%	$108.8313	$108.83	$108.85	$108.80
Purchase #7	$52.45	10.288%	$57.8461	$57.85	$57.85	$57.80
7 purchase totals =	$784.76		$860.0134	$860.01	$860.05	$859.90