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	$246.81	10.793%	$273.4482	$273.45	$273.45	$273.40
Purchase #2	$245.56	3.366%	$253.8255	$253.83	$253.85	$253.80
Purchase #3	$57.85	12.436%	$65.0442	$65.04	$65.05	$65.00
Purchase #4	$45.73	3.504%	$47.3324	$47.33	$47.35	$47.30
Purchase #5	$144.47	9.776%	$158.5934	$158.59	$158.60	$158.60
Purchase #6	$99.36	6.473%	$105.7916	$105.79	$105.80	$105.80
Purchase #7	$96.58	7.478%	$103.8023	$103.80	$103.80	$103.80
7 purchase totals =	$936.36		$1,007.8376	$1,007.83	$1,007.90	$1,007.70