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	$49.70	13.233%	$56.2768	$56.28	$56.30	$56.30
Purchase #2	$81.29	9.810%	$89.2645	$89.26	$89.25	$89.30
Purchase #3	$93.70	13.156%	$106.0272	$106.03	$106.05	$106.00
Purchase #4	$235.71	13.801%	$268.2403	$268.24	$268.25	$268.20
Purchase #5	$228.51	12.299%	$256.6144	$256.61	$256.60	$256.60
Purchase #6	$29.85	5.760%	$31.5694	$31.57	$31.55	$31.60
Purchase #7	$245.70	13.249%	$278.2528	$278.25	$278.25	$278.30
7 purchase totals =	$964.46		$1,086.2454	$1,086.24	$1,086.25	$1,086.30