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	$110.59	11.528%	$123.3388	$123.34	$123.35	$123.30
Purchase #2	$213.84	6.822%	$228.4282	$228.43	$228.45	$228.40
Purchase #3	$116.54	10.342%	$128.5926	$128.59	$128.60	$128.60
Purchase #4	$238.42	9.693%	$261.5301	$261.53	$261.55	$261.50
Purchase #5	$50.69	5.858%	$53.6594	$53.66	$53.65	$53.70
Purchase #6	$89.96	13.530%	$102.1316	$102.13	$102.15	$102.10
Purchase #7	$55.86	8.593%	$60.66	$60.66	$60.65	$60.70
7 purchase totals =	$875.90		$958.3407	$958.34	$958.40	$958.30